Direct Msg. Box Binding – Filter Expression Oddities

While working with direct Message Box binding I became stumped with the following error:

error X2186: identifier ‘VALIDATION_COMPLETE’ does not exist in ‘TrackOrderMessage’; are you missing an assembly reference?
error X2007: cannot find symbol ‘VALIDATION_COMPLETE’
error X2163: an ‘activate’ predicate rvalue must be a string, character, boolean or numeric literal
error X2104: illegal ‘activate’ predicate

The resulting fix? wrap your subscription filters in string literals (i.e. “double quotes”) – as error 2163 indicates: ‘the predicate must be a string, character, numeric or boolean literal.’ Nice.