Ftp manager Session expire

Sir Ftp manager always session expire or when i upload files from root so the say :
Internal Server Error

The server encountered an internal error or misconfiguration and was unable to complete your request.

Please contact the server administrator, you@example.com and inform them of the time the error occurred, and anything you might have done that may have caused the error.

More information about this error may be available in the server error log.

use sftp (winscp)

go to cwp > user accounts >> fix permission >>> select user from the drop down menu >>>> hit fix permission