Access 2007 Report

I have trouble creating of SUM of a field with a condition. The expresion I’m using is:

=Sum(Iif([Accept),[Price],0))

I want to get a total of the prices, only if Accept = Yes. Accept is a Yes/No field. Price is Int.

I always get the following error message:

‘You omitted an operand or operator, you entered an invalid character or comma, or you entered text without sorrounding it in quotation marks’

Any help?