Calculation of Interest Based on Running Sum = #Error = I'm Going Crazy

[jrub]

Many thanks for reading. I'm going crazy trying to understand this...

Can anyone help sort out my efforts to calculate an interest value (a straight forward calculation), based on a running sum value? I would like the running sum to detect if it's the first year, and default to a specified value, and start the running sum afterwards.

I've managed to get to the point where I can get the first value, and the interest is calculated, but all other records report the error: #Error and I'm not sure why, any help?

My running balance query formula is the following:

RunningBalance: IIf([StudyYears]=[ReserveParameters]![StartingBalanceYear],[ReserveParameters]![StartingBalance],Val(Nz((DSum("[Interest]+[Contribution]+[Inflation_Adjusted_Expenditures]","Query1","StudyYears <=" & [StudyYears])),0)))

and my Interest formula is the following:

Interest: ([ReserveParameters]![InvestmentRate]*([RunningBalance]-[Inflation_Adjusted_Expenditures]/2+[AnnualContribution]/2))

[meratigoerr]

What type of datafield is [StudyYears] ? and when you say "You found the first year" do you mean the lowest year (as in oldest)?