Well, I've just discovered FengOffice lask week, so maybe my suggestion isn't going to be a really good one
But from my experience, a blank page in a PHP application means that something is wrong but the causes are multiple.
In order to search the origin of the problem, the only thing we can do is to "read" the error logs of the server.
I don't know IIS (Windows), but in Apache (Gnu/Linux and Windows), there's a file called "error.log".
Open it and maybe you'll get an idea of what's happening.
If you're in a shared host (you don't have control of the server), write and e-mail to your support area asking for the logs of your account.
Finally, sometimes the blank page means that there's a memory problem (memory_limit), and/or an execution time issue (max_execution_time).
I hope this may help
