Restoring a Corrupted LumenRT Files?

I have a LumenRT scene that I had setup.  I made a handful of updates and kept saving every 20 minutes or so.  I ran a low quality video that worked great, but was at the fast setting and I wanted to get it updated with a Fine setting.  When I tried closing the file, LumenRT crashed. When i try to reopen the scene, I get the error, "LumenRT could not open the selected scene.  Please ensure that you have enough disk space available. If you do your scene may have been corrupted."  When i closed the file ,i realized i was indeed low on disk space, which i then cleared out 10 free gigs.  

I've tried copying the .bak file, to a different name and changing .lrt file, but get the same error.  Is there anything else I can try to restore my scene?  

Any help would be great.  I have a public meeting tomorrow and don't have the time to set everything up again and troubleshoot, so worst case i can just use the Fast quality version.  

Thanks,

Brian