Why does your code have two DistinctCount functions?
Also databse fields are always enclosed within curly braces like this:
{tblPurOrdersHis.db_DateRec}
In your code above both the fields have a round brace - The first field has a round brace to the end and the next one has one at the start. Please correct that too.
Have a look at the code I posted above.
-Abhilash