Ken Slovak wrote:
That could do it. I don't know if an error handler would help, it
certainly should be used in any case as a good practice.

Just now, one minute ago, while working on email, a message box popped up

"Rules in Error"

There is no information what is in error and the only option is Close

the test rule was thus unchecked in the Rules list and I had to go back and
manually check it again.

I have an On Error Goto Exit: in the start of the Sub and it's been happily
running all day long
Apparently that is not enough to keep the rule turned on and I wish I could
tell what was the error?