A 500 error is a generic error that literally means "An error has occurred", it really doesn't give us anything to go on to find the cause of the problem.
Does the error display when you load the page, or only after submitting?
Are you sure all of the files are uploaded, including the WA_SecurityAssist and Connections folder?
Did you update the connection file to reflect the server environment?
can you send a link where we can see the problem and a copy of the login page.