Synopsis
You specified an invalid variable stem name.
Cause
You used a DO OVER loop, but didn't specify a stem name (ie, must end with a dot) after the OVER keyword.
Cure
Make sure you specify a legal variable name which ends in a dot, after the OVER keyword.
Cause
An add-on library, Exit handler, or Environment was passed a stem name by your script, but that stem name is not valid.
Cure
Consult the documentation for that product to see what arguments you should be passing to a particular function/command that you're trying to use in that add-on library, Exit handler, or Environment. Look up this error message in that documentation. Check that you have the latest version of the software.