#Error in SSRS, Tried CSTR to convert but no impact

Kindly help!

=IIF(ISNOTHING(CStr(Fields!ExpAccountDisplay.Value)) OR CStr(Fields!ExpAccountDisplay.Value) = 0 OR CStr(Fields!ExpAccountDisplay.Value) = “”,”No Exp Account”,CStr(Fields!ExpAccountDisplay.Value))

The data type of field is uniqueidentifier.

The Value to the field from application is Advertising Expense – 6100