QT app on several win32 computers

Hi,
we're working on a Qt graphics app, dlRaw.
It works fine with linux and it compiles and works fine with win32 (mingw), but only on the machine it was built.
Everything on WinXP:
So, I copied the needed files to a new directory, on the same computer and it works fine from there, so all dlls are there. If I copy the whole directory to another computer, it doesn't work there, it gives some error related to qtgui4.dll:
Problemsignature:
AppName: dlraw.exe AppVer: 0.0.0.0 ModName: qtgui4.dll
ModVer: 4.5.1.0 Offset: 000bd056,
and an attached text file, which I attached to this thread. It also doesn't work (with the same error), if I use the files from the built directory via network...

We had an earlier version which worked without problems, on other WinXP computers, but there were no significant changes in between, the only thing was an additional library, ImageMagick...

What bothers me most, it works fine on the computer it was built with, but is not every windows the same? Both are WinXP with SP 2 and latest updates...

Any ideas?

greets mike