Aggregate function in Excel w/s does not work for data written from C#

Question

I am writing a string array to Excel from C# using the Range.Value2 method. After transfering the data to Excel when I try to do a sum of range of numeric values the result is 0. Even if i do a sum on one cell that has a numeric value the result is 0. Is there something else that needs to be done during the transfer?

Thank you.