Why do I get "error 2" when returning a borrowed license?

When I try to return a borrowed license to the license server early, why do I receive an "error 2"?

Answer 1

[MathWorks Support Team]

If there is another, invalid license on the search path, returning the borrow key will give you an error 2. The server sees the toolbox as returned, but the client holds on to the key. Removing the invalid license should resolve it.