diff --git a/fields/fields_edit_new.php b/fields/fields_edit_new.php
index aaa3eba..eb40fc9 100644
--- a/fields/fields_edit_new.php
+++ b/fields/fields_edit_new.php
@@ -125,7 +125,7 @@ function setValueList() {
 );
 
 $form->addCheckbox('imf_mandatory', $gL10n->get('SYS_REQUIRED_INPUT'), (bool)$itemField->getValue('imf_mandatory'), array(
-    'property' => $itemField->getValue('imf_system') == 1 ? HtmlForm::FIELD_DISABLED : HtmlForm::FIELD_DEFAULT,
+    'property' => HtmlForm::FIELD_DEFAULT,
     'icon' => 'fa-asterisk'
     )
 );
@@ -144,5 +144,5 @@ function setValueList() {
 ));
 
 // add form to html page and show page
-$page->addHtml($form->show(false));
+$page->addHtml($form->show());
 $page->show();
diff --git a/import/import_column_config.php b/import/import_column_config.php
index 4b21041..1305caf 100644
--- a/import/import_column_config.php
+++ b/import/import_column_config.php
@@ -91,15 +91,12 @@ function getColumnAssignmentHtml(array $arrayColumnList, array $arrayCsvColumns)
     return $html;
 }
 
-$items = new CItems($gDb, $gCurrentOrgId);
-$items->readItems($gCurrentOrgId);
-
 // create html page object
 $page = new HtmlPage('admidio-items-import-csv', $headline);
 $page->addHtml('<p class="lead">'.$gL10n->get('PLG_INVENTORY_MANAGER_IMPORT_ASSIGN_FIELDS').'</p>');
 
 // show form
-$form = new HtmlForm('import_assign_fields_form', ADMIDIO_URL . FOLDER_PLUGINS . PLUGIN_FOLDER_IM . '/import/import_items.php', $page, array('type' => 'vertical'));
+$form = new HtmlForm('import_assign_fields_form', SecurityUtils::encodeUrl(ADMIDIO_URL . FOLDER_PLUGINS . PLUGIN_FOLDER_IM . '/import/import_items.php'), $page, array('type' => 'vertical'));
 $form->addCheckbox('first_row', $gL10n->get('SYS_FIRST_LINE_COLUMN_NAME'), $formValues['first_row']);
 $form->addHtml('<div class="alert alert-warning alert-small" id="admidio-import-unused"><i class="fas fa-exclamation-triangle"></i>'.$gL10n->get('PLG_INVENTORY_MANAGER_IMPORT_UNUSED_HEAD').'<div id="admidio-import-unused-fields">-</div></div>');
 
@@ -147,31 +144,31 @@ function getColumnAssignmentHtml(array $arrayColumnList, array $arrayCsvColumns)
             </tr>
         </thead>';
 
-        $arrayCsvColumns = $_SESSION['import_data'][0];
-        // Remove only null values
-        $arrayCsvColumns = array_filter($arrayCsvColumns, function ($value) {
-            return !is_null($value);
-        });
+$arrayCsvColumns = $_SESSION['import_data'][0];
+// Remove only null values
+$arrayCsvColumns = array_filter($arrayCsvColumns, function ($value) {
+    return !is_null($value);
+});
 
-        $categoryId = null;
-        $arrayImportableFields = array();
-        
-        $items = new CItems($gDb, $gCurrentOrgId);
-        $row = array();
-        foreach ($items->mItemFields as $columnKey => $columnValue) {
-            $imfName = $columnValue->GetValue('imf_name');
-            
-            // If the field name starts with 'PIM_', it is a language key
-            if (strpos($imfName, 'PIM_') !== false) {
-                $row = array($columnValue->GetValue('imf_name_intern') => $gL10n->get($imfName));
-            } else {
-                $row = array($columnValue->GetValue('imf_name_intern') => $imfName);
-            }
-            
-            $arrayImportableFields[] = $row;
-        }
+$categoryId = null;
+$arrayImportableFields = array();
+
+$items = new CItems($gDb, $gCurrentOrgId);
+$row = array();
+foreach ($items->mItemFields as $columnKey => $columnValue) {
+    $imfName = $columnValue->GetValue('imf_name');
+    
+    // If the field name starts with 'PIM_', it is a language key
+    if (strpos($imfName, 'PIM_') !== false) {
+        $row = array($columnValue->GetValue('imf_name_intern') => $gL10n->get($imfName));
+    } else {
+        $row = array($columnValue->GetValue('imf_name_intern') => $imfName);
+    }
+    
+    $arrayImportableFields[] = $row;
+}
 
-        $htmlFieldTable .= getColumnAssignmentHtml($arrayImportableFields, $arrayCsvColumns) .'
+$htmlFieldTable .= getColumnAssignmentHtml($arrayImportableFields, $arrayCsvColumns) .'
         </tbody>
     </table>';
 $form->addHtml($htmlFieldTable);
diff --git a/import/import_items.php b/import/import_items.php
index f7eb1e5..6c607e5 100644
--- a/import/import_items.php
+++ b/import/import_items.php
@@ -1,4 +1,3 @@
-
 <?php
 /**
  ***********************************************************************************************
@@ -41,16 +40,19 @@
  */
 function compareArrays(array $array1, array $array2): bool {
     $array1 = array_filter($array1, function($key) {
-        return $key !== 'KEEPER' && $key !== 'LAST_RECEIVER' && $key !== 'CATEGORY';
+        return $key !== 'KEEPER' && $key !== 'LAST_RECEIVER' && $key !== 'CATEGORY' && $key !== 'IN_INVENTORY';
     }, ARRAY_FILTER_USE_KEY);
 
     foreach (['RECEIVED_ON', 'RECEIVED_BACK_ON'] as $dateField) {
-        if (isset($array1[$dateField])) {
+        if (isset($array1[$dateField]) && $array1[$dateField] !== '') {
             $date = DateTime::createFromFormat('d.m.Y', $array1[$dateField]);
             if ($date) {
                 $array1[$dateField] = $date->format('Y-m-d');
             }
         }
+        else {
+            unset($array1[$dateField]);
+        }
     }
 
     foreach ($array1 as $value) {
diff --git a/import/import_read_file.php b/import/import_read_file.php
index 16d7b11..fc1dd23 100644
--- a/import/import_read_file.php
+++ b/import/import_read_file.php
@@ -12,7 +12,6 @@
 
 require_once(__DIR__ . '/../../../adm_program/system/common.php');
 require_once(__DIR__ . '/../common_function.php');
-require_once(__DIR__ . '/../classes/items.php');
 
 // Access only with valid login
 require_once(__DIR__ . '/../../../adm_program/system/login_valid.php');
@@ -73,12 +72,6 @@
 // => EXIT
 }
 
-$items = new CItems($gDb, $gCurrentOrgId);
-$items->readItemData($getItemId, $gCurrentOrgId);
-
-// read file using the phpSpreadsheet library
-//$_SESSION['rol_id']           = (int) $items->getValue('rol_id');
-
 switch ($postImportFormat) {
     case 'XLSX':
         $reader = new \PhpOffice\PhpSpreadsheet\Reader\Xlsx();
diff --git a/items/items_delete.php b/items/items_delete.php
index 2b1471a..b72956d 100644
--- a/items/items_delete.php
+++ b/items/items_delete.php
@@ -107,7 +107,7 @@ function displayItemDeleteForm($items, $user, $getItemId, $getItemFormer) {
 		$form->addCustomContent('', '<br />'.$gL10n->get('PLG_INVENTORY_MANAGER_ITEM_MAKE_TO_FORMER'));
 	}
 
-	$page->addHtml($form->show(false));
+	$page->addHtml($form->show());
 	$page->show();
 }
 
diff --git a/items/items_edit_new.php b/items/items_edit_new.php
index bfa4c7e..edb22ab 100644
--- a/items/items_edit_new.php
+++ b/items/items_edit_new.php
@@ -434,5 +434,5 @@ function isSelect2Empty(selectId) {
     (int) $infoItem->getValue('imi_usr_id_change'), $infoItem->getValue('imi_timestamp_change')
 ));
 
-$page->addHtml($form->show(false));
+$page->addHtml($form->show());
 $page->show();
\ No newline at end of file
diff --git a/items/items_history.php b/items/items_history.php
index 32a5555..367531f 100644
--- a/items/items_history.php
+++ b/items/items_history.php
@@ -91,7 +91,7 @@
 $form->addInput('filter_date_to', $gL10n->get('SYS_END'), $dateToHtml, array('type' => 'date', 'maxLength' => 10));
 $form->addInput('item_id', '', $getItemId, array('property' => HtmlForm::FIELD_HIDDEN));
 $form->addSubmitButton('btn_send', $gL10n->get('SYS_OK'));
-$FilterNavbar->addForm($form->show(false));
+$FilterNavbar->addForm($form->show());
 $page->addHtml($FilterNavbar->show());
 
 $table = new HtmlTable('profile_field_history_table', $page, true, true);
diff --git a/preferences/preferences_function.php b/preferences/preferences_function.php
index ad558b5..7542d18 100644
--- a/preferences/preferences_function.php
+++ b/preferences/preferences_function.php
@@ -124,7 +124,7 @@ function showDeinstallationDialog() {
 	$form->addSubmitButton('btn_deinstall', $gL10n->get('PLG_INVENTORY_MANAGER_DEINSTALLATION'), array('icon' => 'fa-trash-alt', 'class' => 'offset-sm-3'));
 
 	// add form to html page and show page
-	$page->addHtml($form->show(false));
+	$page->addHtml($form->show());
 	$page->show();
 }