QPSQL driver in windows

[Methedrine]

My folder structure looks like this for the release version:

./myapp.exe
./comerr32.dll (version 1.3.5.0)
./krb5_32.dll (version 1.3.5.0)
./libeay32.dll (version 0.9.8.1)
./libiconv-2.dll
./libintl-2.dll
./libpq.dll (version 8.1.5.6286)
./ssleay32.dll (version 0.9.8.1)
./sqldrivers/qsqlpsql.dll
./qtcore4.dll
./qtsql4.dll
./qtgui4.dll

./myapp.exe
./comerr32.dll (version 1.3.5.0)
./krb5_32.dll (version 1.3.5.0)
./libeay32.dll (version 0.9.8.1)
./libiconv-2.dll
./libintl-2.dll
./libpq.dll (version 8.1.5.6286)
./ssleay32.dll (version 0.9.8.1)
./sqldrivers/qsqlpsql.dll
./qtcore4.dll
./qtsql4.dll
./qtgui4.dll

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This works perfectly fine. However, keep in mind that a debug build of your software should link against the debug qt libs (this includes the debug build of qsqlpsql.dll!).
Considering that my libpq is a lot more recent than yours, I would not rule out the option that that might be a source of trouble, too.