Looks like you have an unstored calculation field on the wrong side of the relationship. Fields on the "many" side of a relationship must be indexed, stored fields and a calcualtion field that refers to global fields cannot be stored.
But I think you are over complicating your design.
You should be able to use this relationship:
Diary::gStartDate < Diary 2::Date AND
Diary::gEndDate > Diary 2:: Date
Thanks very much Phil. I had not thought about placing the calculation into the relationship.
That works perfectly. I appreciateyour help.