Running Value error

[giggles7840]

Im new to SSRS 2008. I am using SQL Server 2008.

I am trying to create a column that has a running total based on the change of an existing column (date).

An example would look like this:
1 8/5
1 8/5
1 8/5
1 8/5
2 8/6
3 8/9
3 8/9

Right now i am trying tyhis:
=RunningValue(Fields!TargetDate.Value,Sum,"TargetDate")

However I keep getting a #Error

What am I doing wrong? "TargetDate" is a group I created.

 

[giggles7840]

duh. cant sum a date. totally overlooked that. nvrmind.

 

[giggles7840]

ok im wrong its still not working.
I changed it to:
=RunningValue(Fields!TargetDate.Value,Count,"TargetDate")

It is counting however, on the change of Fields!TargetDate.Value it is not moving to the next increment.

What do i do?