Media Encoder won't add a job from Premiere that requires the overwriting of an existing video file.

I have a few mp4 files which did not encode correctly from Media Encoder. I did an update. When I redo those exports within Premiere, tell it to Send to Media Encoder, then tell it to overwrite the existing file. It fails to add the job to teh Media Encoder queue. Maybe it has something to do with switching Beta versions between exports. Not sure.