No, the empty string won't affect the filter.
Did you test both the control date, and a date in a record?
Did you use an absolute reference to the control date in the criteria
formula?

R. Choate wrote:
It tested as a legitimate date. I perhaps should mention that some of the cells in the column returned zero-length text because the
formula calls for that if the precedent cell is blank. I don't know if that affects anything.


--
Debra Dalgleish
Contextures
http://www.contextures.com/tiptech.html