Error: A summary has been specified on a non-recurring filed

I have a report that I am using to determine audit results. There are 6 report fields that contain the results of the audit. The first 4 fields are the original audit results:

1.TP Cost

2. TP FCV

3. Assr Cost

4. Assr FCV

The next 2 fields are the proposed corrections.

5. Proposed Cost

6. Proposed FCV

The last report field @difference2 calculates the difference between the TP FCV - Proposed FCV. In some cases there was a no change meaning that the Proposed Cost and Proposed FCV are 0. What I would like to do is the following formula.

//if

//Sum ({qryAuditSummary.Proposed FCV}, {qryAuditSummary.Year})= 0 then

//{qryAuditSummary.TP FCV}-{qryAuditSummary.Assr FCV} else

{qryAuditSummary.TP FCV}-{qryAuditSummary.Proposed FCV}

The above formula evaluates if the sum of the proposed FCV; if it is 0, then it will calculate the orignial audit results, if not 0, it will calculate the proposed audit results.

When I do this I get an error message Error: Error: A summary has been specified on a non-recurring filed.

Is there a way to work around this?