The default location on a machine with qRules installed is C:\Program Files (x86)\Qdabra Software\Qdabra Rules Library\DLLs, although depending on where qRules was installed, this could vary. If you save the form template as source files (Publish > Export source files) it should also be present in the source files. If dropping the DLL into the folder doesn't work, you may want to try deactivating the template (or even completely removing it) from Central Admin and publishing again.
Hilary Stoupa
