Getting "expect: option requires..." error

[flaugher]

When I use vim-sync and type my leader key followed by "su", I get the following error:

expect: option requires an argument -- c    
usage: expect [-div] [-c cmds] [[-f] cmdfile] [args]
shell returned 1.
Press ENTER or type command to continue

I copy-pasted the sftp code as shown into an executable .sync file and then changed "login_name" and the 1.2.3.4 IP address to my login name and the server's IP address.

Any ideas on how to fix this?

Thanks.