New Post: System.NotImplementedException: DATEDIF

I have a spreadsheet containing a DATEDIF formula within a cell. When I attempt to evaluate the formula, I get the above error. I've tried this with both HSSF and XSSF, with both the EvaluateAllFormulaCells and workbook.GetCreationHelper().CreateFormulaEvaluator().EvaluateAll() sub routines.

I've examined the source code of the project and it does appear that the DATEDIF function has been written as part of it, so I can't figure out why this isn't working.

Has anyone had a similar problem or know what the solution is?

Thanks