FTP users can not login using vsFTP server
Make sure that vsftp has been setup in pam files.
vsFTp has additional configuration which can restrict user's access. The default configuration will allow QAS user's to login as the option "userlist_deny" in the vsftp.conf is set to YES. This will allow all users EXCEPT user's that are listed in the userlist_deny file to access the FTP server.
If you have changed the userlist_deny option to NO then this will deny ALL user's access to the server EXCEPT user's the are listed in the userlist_deny file.
If you continure to have problems with user's accessing vsFTP, please contact the vendor for further assistance.