When I print the value of errorString from my QPluginLoader object, I get this: The file 'C:/pyprojects/test/qsqlpsqld4.dll' is not a valid Qt plugin. I would like to avoid some days worth of doing the time consuming "guess-and-check" methodology that my current internet searches reveal (so far none of them seem relevant anyways). Is there a way for me to get the Qt library itself to tell me why it is refusing to load this plugin? I don't want to guess; I want to know. Context: I am on Windows 7 running Qt 4.8.5 (32-bit, MinGW) and the qsqlpsqld4.dll file is also 32-bit and compiled with MinGW. I am using PySide to interact with Qt.