IWP issue: users get blank white screen at login

Another IWP problem...

At various points some IWP users will enter their login information, but then only get a blank white web page as a result. No error messages, no 'Database Homepage' default page, nothing. Their names don't appear to show up in the Server client list even. This problem does not affect all users equally or at the same time. Sometimes some people get the error, while others at the exact same time do not.

Does anyone know if users have to FINISH the "On File Open" script before being considered 'logged in' (that is, showing up in the logs and on the Server's client list)? I am wondering if this is a problem with our login script or with IWP itself. We have made various changes to the script to try and narrow it down, but haven't had conclusive results.

The error also seems to be correctable, at least temporarily and depending on what browser is being used, by clearing cookies. (I have even instructed many people to block all cookies for our website if using Firefox.)

Sometimes a different browser works, sometimes they try again later and it works, clearing cookies sometimes works...

Thanks,

- J