Excel function in VBA

Hi guys, I'm trying to call the function "mduration" in VBA. It outputs the correct numbers but it always says: "type mismatch" after performing the calculations.

Here's the code:

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Cell.offset(0,14).value refers to yield. It has the following code which works fine:

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Any suggestions as to how to combat the type mismatch error?

Do you want the result in the cell?
[code]
Cell.Offset(0, 15).Value=application.WorksheetFunction.MDuration(etc
[/code