Thanks for replying.
Actually I didn't wrote report but I am responsible to do some changes and get it work back.
Let me describe my problem in detail again.
I am using query as source of report. So the result of query is different(means different number of field). every time.
eg. field name like 1st, 2nd, 3rd. sometime the query results like 1st, 2nd.
I used 3rd filed in the formula. So when program runs and not find 3rd field, it gives error. So is ther any way to check the field availablility like it exist or not in the code any where.