Comment: When you open an existing file with Rhino, a second file with the same name with an added “.rhl” extension is also created. This Rhino Lock keeps other Rhino users from opening the file while you have it open.
Normally these files are deleted within a few seconds of the Rhino file being closed. If you try to delete them while the file is still open you will get a warning message and the system will refuse.
A user recently reported that if Rhino is open, and the IObits SystemCare utility is run, it changes file permissions so Rhino is blocked from deleting its own lock file.
This results in Rhino warning you the file is in use when it really isn't, and these RHL files stack up.
He also reported a second cause. Apparently Avast anti-virus has a tool for scanning file when being written. This too was blocking Rhino from deleting it's own RHL files.
-John Brock 6.15.2011
Another cause of .rhl files being left on your computer is a Rhino crash - the file gets left behind because Rhino crashed before it had a chance to delete it. In that case, it is perfectly safe to manually delete the orphaned .rhl file. –msh 24.06.2011