When you say the Criteria is FX, I'm guessing that that is the name of a field in your table and also the name of a control on your form/report?
I don't know what data type FX is though.
If it's a number:
=DCount("[EXP]", "TBLTABLEQUERY2", "[FX] = " & [FX])
If it's text:
=DCount("[EXP]", "TBLTABLEQUERY2", "[FX] = """ & [FX] & """")
If it's a date:
=DCount("[EXP]", "TBLTABLEQUERY2", "[FX] = #" & [FX] & "#")