Basics first: Windows 7 Home Premium, 64 bit architecture. No other wallpaper software, no non-standard windows themes. I am extending the taskbar (which sits at the top of my screen) across both

When I try to move a maximised window from one monitor to the other by dragging the title bar, I get a pop-up error saying that "WM_SIZING contains bad value." Clicking okay on this error message returns the window to the original monitor in a restored (not maximised) state.

I can move windows from one monitor to another if the window is not maximised in the first place, and I can move them by adding buttons to the title bar, just not be dragging the title bar. Can you help?

One further bit of info, which might or might not be pertinent:
monitor 1 = 1680 x 1050
monitor 2 = 1440 x 900

No Problem.

Only when I try to move a maximised window from one monitor to the next -- which is only possible when running DisplayFusion, right? So I've never tried to replicate it when DisplayFusion is not running.

I have DF set to run whenever windows runs.

Hrm.... only some windows it appears.

Can move
Q-Dir
Winrar
Windows Explorer
Songbird
Excel
Word (and I assume the rest of MS Office)
Paint.NET

Can't move maximised
Firefox
Internet Explorer
Songbird
Opera
Google Chrome
Windows Live Writer

Could it possibly have something to do with x86 applications on a x64 machine? 32-bit applications are stored in C:\Program Files (x86), whereas 64-bit applications are stored in C:\Program Files

Just a random thought.

Just tested -- I still get the error when DisplayFusion is not running.

Found the problem... it's a problem with a little program called allSnap. Since that's a bit redundant on Win7, I'm uninstalling it now.