Process Flow Date Calcs not working

I have a process flow in which I'm trying to create a new 6 Month Eval that occurs 6 months after the effective date of the action. Under the Start activity node, I'm able to make the following declairation:
revDateSixMo=getDateDME(AddMonth(pfDate(Effect_Date),6))

The result is: empRevDateSixMo(Type=String) = 07/09/2011

It works under the Start node. However, later in the process flow, I check to see if the effective date has been changed and I try to re-calculate the same date in an Assign activity node. It always throws an error: "01042011 is not a function". I've broken down the statement into individual commands, and cannot seem to get a date type result from date=pfDate(Effect_Date).

I am using Designer v9.0.1.3. Does anyone have a solution for this?