Calculated Fields in Report Dataset

I'm creating an easy report on invoices, I have my invoices grouped by type with a count of all projects in that group and a sum of all invoice amounts in each group. I have a grand totals field in my report footer with a SUM(Fields!COUNT.Value) and SUM(Fields!AMT.Value) to give me grand totals of all amounts and grand total of all invoices in all groups. My problem is that I need to have a percentage of the total shown in each invoice type group. So if I have 100 invoices and 10 are type A then the type A group should show 10%. If I enter the calculation of (Fields!Count.Value)/(SUM(Fields!Count.Value) it will divide 10 by 10 for group A since it's in the group. For some reason, if I create a calculated field in the dataset with the calculated value of =SUM(Fields!COUNT.Value), I get an error when trying to preview the report. Can anyone help?

Nevermind, I created a second dataset without the group by and used those numbers for my division problems.