Restarting Excel and Windows
Even now sometimes a full restart is a possible solution.
I recently had a macro returning a weird error message about an action taking too long. Restarting Excel did not fix it.
So, I restarted Windows and the macro worked as expected.
These days with so many apps running in the background, sometimes the only solution is a restart of Excel and Windows.
Turning it off and turning it on can still solve issues.