run-time error 13: type mismatch in VBA (Excel 2007)

hello,
I'm writing a VBA program and receive "run-time error 13: type mismatch"

this is the code in bold where it happens:

        Let FactornEMA(nEMA) = 2 / (FactorMA(nEMA) + 1)   'run-time error 13: type mismatch
              
        Let Cells(1 + nData, colEMA(nEMA)) = FactornEMA(nEMA) * (Cells(1 + nData, 4) - Cells(nData, 4))
              
        Else
        End If

For clarification, FactorMA(nEMA) is an array of about 2 possible values a and b.

I have all parts of the line defined as variables and I use that calculation as a constant in the next line.
Can somebody tell me why I receive this error?
Thanks.

You need to post more code, we don't know how you have dim'd any of the variables in the post, nor what values they might be holding when the error crashes it.

I resolved the message.
Thank you for your help!