subtotal & grandtotal subforms

[stormin_norm]

I have a form with the following:
student name, college id (what colleges the student previously attended)

the subform contains the courses attended at the particular college. Each course is marked as 3 credits for english, or 3 credits for history, etc...

In the footer section I total all the English credits, and all the History credits for that college (subtotal).
first error--> I then try to total up all credits for that particular college in the footer as:
txtboxCollegeTotal
Control Source =[ENGsubtotal]+[HISsubtotal]+....etc.

I get the courses to subtotal, but the college total is typically blank, and once in a while zero.
Is there a better technique?


Stumper--> Best method to sum ALL subtotals into a grand total on a form. I get ERR in the subform when using the Control Source method. Naturally a sum query works great, but I want it to be dynamic, so when additional transcript info is entered, the total will be dynamically adjusted.

On a report it would look like this:

Student: Mary Jane Pahrtier
College: Yuengling College
Course ENG HIS PHI
1 HIS100 3
2 ENG200 3
3 ENG201 3
Subtotal 6 3 0
Total for Yuengling College: 9 credits

College: Bittberger State
Course ENG HIS PHI MTH
1 PHI100 3
2 ENG333 3
3 ENG444 3
4 MTH100 3
Subtotal 6 0 3 3
Total for Bittberger State: 12 credits

Total Credits for May Jane Pahrtier: 21 credits

Thanks!
-Stormin'