Global Search Error When Adding Rev Found Field

We are writing a global search that looks for a particular title.block.Number.  When clicking on the 'More' button we can add more fields to display.  The fields I have listed are Title.Block.Number, Title Block Description, Title Block Phase,  Title Block Document Type, Events - CAPA.Number, Events, CAPA.Failure Mode, Events-CAPA. Originator, and Title.Block.Rev.  

This global search works fine and returns the information correctly.

When I add Events-CAPA.Rev Found to the list above I get an error message that states 'Fail to convert internal representation'.

More background:  the object type is Documents and the Search Type is Object Search.