On Sunday, May 4, 2014 9:40:48 AM UTC+10, Matt Herron Jr. wrote:
I upgraded to 5.12 which apparently has LOTS of serious problems. I attempted to upgrade to 5.15 but Windows said the installer was "not a valid 32 bit application". Now I just want to downgrade to a stable release. Any ideas?

That's because you are trying to install the program onto your PC, not the Oudie. Copy the updater file to the top level directory of your Oudie then restart it.
The instructions for doing this are on the web site.