Are you *really* sure that you've cleaned and rebuilt *all* binaries? From what you've described here, it looks like somewhere (whether it's your own app/dlls or qwt), you still have a binary that was built against a newer version of Qt than you're loading at runtime.

Note that your unresolved symbol - QLayout::setAlignment (I assume you meant "QLayout" and not "Layout"?) had a new overload added for Qt 4.3. If you have a binary that was built against Qt 4.4 and uses this overload, this could explain why you're having trouble with loading Qt 4.1.

You can use Dependency Walker (depends.exe) on Windows to track down the problem binary. Open your executable in Dependency Walker and profile it. You should see exactly which binary has the missing dependency, and then rebuild that binary.

HTH,
-Chris