A blank screen in Roundcube is an indication of a PHP error that gets logged into the log file on the server but isn't shown to the user.

In order to find out what the problem is, you need to look into the Roundcube error log, which is usually located here:

[roundcube]/logs/errors

Make sure that the server can write to the log file, otherwise you won't be able to find out what's wrong.

Once you see the detailed error, it will give you an indication of what's wrong. Maybe a directory or a file has wrong server permissions, or there is an error in one of your config files... There are thousands of things that could be wrong, and knowing the specifics of the error is the first step to getting it solved.

You can also check the browser console to see if there are any javascript errors.

If you cannot resolve the problem by yourself, create a support ticket and our staff will get back to you as soon as possible. But please make sure to include the error you found in the error log, otherwise our techs won't know what's wrong either.

It might also be helpful if you create a test email account so our techs can log in to your Roundcube and see the error first hand.