plesk mail server settings - get Internal error ";-P"

Ran upgrade Plesk Obsidian Version 18.0.21 to 18.0.23 - OK

Went to Tools & Settings / Mail server settings
Got error message Internal error ";-P" with OK and CANCEL buttons.
Clicked cancel - try again, same error message.
Clicked Ok and got into Mail server settings
Saw Enable mail management functions in Plesk checkbox not checked.

Checked Enable mail management functions in Plesk checkbox.
Clicked Ok - seemed to work.
Went back...

plesk mail server settings - get Internal error ";-P"