SmartFTP 6.0.2117.0 - Connection=The system cannot find the file specified

We have just upgraded to the new 6 version (from 4.1). Users reports that they receive: "The system cannot find the file specified" when they hit the Connection button. 
How could we resolve this?
Thanks in advance!
Best regards,

Install the latest version
Then ensure that SmartFTP is not blocked by a software firewall and antivirus product. Make sure that no registry entries are deleted by any 3rd party products.