Notes Error

I was switching between Client, Designer and Admin (using 8.5.3 FP1) when this occurred.

"Notes IPC Asynch Message Processor (16)". It seems to stem from the fact that it couldn't open the search bar in my mail file. Actually this is not surprising as what I was also doing was using Location documents to switch between my ID, and an Admin ID whilst upgrading a database design.
IBM have a technote http://www-01.ibm.com/support/docview.wss?uid=swg1LO48522

A programming error was found but will not be corrected. It will be a permanent restriction.

All well and good, but being the Geek I am' I'd still like to know what the exact cause is. I can make a guess that it's the Inter Process Communications transfer. I wonder if one process is in one ID and another process in a different ID. Just as well they shouldn't talk to each other as it could open a whole can of worms.