I see this as two related changes:

a) Leave the module name query box open when there is a error, so the user can either correct a mistake (or hit Cancel) without reopening the box and re-entering the module name.  Good idea.

b) Put the error message in the box itself, perhaps with a beep.  I presume there would be no [OK] button, but rather the cursor would remain in the entry box.  Nice simplification.

I believe 'not a source-based module' means 'not a python-coded module', which seems a little clearer. We could check the importlib doc.