Weird behavior on window.open

After migration to a new server (win 2008 R2 from win 2003) - Design studio form with script that simply opens a popup window and writes content does not work. The window.open does actually open the popup, but the following document.write (even with simple "test" string) hangs when trying to write to the window. This is not contained to one form - happens anywhere you try it in DS. But couple of strange things - this works on new test server - same OS/Env, etc.... And ESS custom for with same window.open and document.write works on both servers - and all in same browser so no IE security differences. So something regarding the new object being created in design studio form on production server that seems to be causing this. First thought is permissions somehow somewhere but can't trace that down. Token is not secured - and function to open new window is not one of the standard events - just a function called Print() - no parameters passed.

If the window.open call is changed to _parent then it works fine and content displays in the page - so its just contained to a new blank window.

Thoughts?