I will admit that this message is not very helpful, but you are getting this message because you are mixing apples and oranges. You are trying to do running totals both the easy way and the hard way at the same time.
The evaluate condition in a running total field tells it WHEN to increment, not WHAT to increment. You simply want to have the following evaluate formula:
InStr ({new_combine.F_S}, "."

=0 and
Mid ({new_combine.F_S}, 7, 1)="01"
You tell it WHAT to summarize in the FIELD TO SUMMARIZE setting, and then pick the operation SUM if you want to accumulate them.
The formula that you are using would be a good running total as a stand-alone formula. This is how we did it before there were running total fields. The only type was the last = should have been := which is the CR asssignment operator.
For more info see the FAQ on running Totals.
Ken Hamady
On-site custom Crystal Reports Training and Consulting.
Quick Reference Guide to using Crystal in VB.