Any ideas what "Invalid Formula Structure" on right-click in calendar means

When trying to get the right-click pop up menu so I can look at a document properies (from the calendar), I get an error pop-up box saying “Invalid Formula Structure” with title “IBM Lotus Notes”. If I go the long way, and open the document, or go via File > Application > Properties, it works OK. Only the direct right-click fails.

Anyone seen this before??? It’s not reported in this forum.