MCF dialogs won't open in unity

since upgrading to unity 3.3 from 2.6 Iv had a very very annoying bug in unity. no MFC dialogs are getting launched from the menus.

This includes File->Open Scene File->Save Scene As and most annoyingly File->Build & Run and Build from the build settings dialog

when I click on any of these nothing opens no errors or anything.
I'm running the full version of unity pro on windows 7 64bit.

on a side note, Unity also has trouble seeing a x64 version of p4merge, the drop down list is empty, if I install a x86 version of perforce it sees it fine. I only note this because its not the case for my friends copy which works fine, he installs the save x64 version of p4 merge and it show up fine.

Iv tried everything I can think of and haven't been able to get this to work. has anyone seen any issues like this, or knows how to fix it?