I made a mistake and had to abort a recode. But when I tried to delete the partially created file, the OS complained that the file was still open by VideoReDoEncoder64.exe. Even though VRDPro was no longer running, that program still was. Oops!
In the newer versions we've switched to a system where the encoders are run in a secondary process, rather than in the main one. We do this because it allows us to compile the encoder process as 64bit without having to compile the main VRD process as 64bit, which is not currently possible due to the use of some 3rd party libs which aren’t available as 64bit. So if you force quit you'll have to kill both processes.