Error "Event not handled" when searching for data with AppleScript

Hi,

first post here.

Got a problem with a very simple AppleScript that I'm very sure that was working once upon a time:

tell application "FileMaker Pro Advanced"

return every record of table "Mail" whose field "InternalMessageID" is "<[email protected]>"

end tell

The error is:

error "FileMaker Pro Advanced got an error: Event not handled." number -1728 from every record of table "Mail" whose field "InternalMessageID" = "<[email protected]>"

I found a topic here on this forum with a similar error (http://fmforums.com/forum/topic/93624-applescript-grabbing-value-from-related-table/). But unfortunately, there was no solution posted.

Does anyone have an idea what might cause this? The file is open and is in browse mode. 

Regards

Beatrix Willius