Blank page when impersonation is used

[Frank]

Hi,

All of a sudden the default.aspx page of our application returns with a
blank page (view source is completely empty). Our application is running with
impersonation enabled because it needs to use Word.
There are no error messages in the event viewer and the IIS log reports a
200 response code. When disabling impersonation the default.aspx page
displays normally.

Any ideas where to look that might be causing this?