[voltagex_]

I found a bug with an offline documentation reader (can't remember which) that if you pack one of the QT components (qwindows.dll) the application wouldn't load anymore. Still not sure whether to report a bug and who to report it to.

Yes UPX is cool, but I don't think it's 100% compatible.

[ultramancool]

You can usually set UPX options to fix that kind of thing. You may have stripped necessary linking information. I usually use it on statically linked things though, so no issue there.