YEARFRAC Error in calcualation.

[Mavericks334]

Hi,

I have two columns that give me the dates.

I am using YearFRAC to calculate the difference in years.

[TABLE="width: 116"]
<COLGROUP><COL style="WIDTH: 62pt; mso-width-source: userset; mso-width-alt: 3035" width=83><COL style="WIDTH: 54pt; mso-width-source: userset; mso-width-alt: 2633" width=72><TBODY>[TR]
[TD="class: xl74, width: 83, bgcolor: #92cddc"]Joining Date[/TD]
[TD="class: xl74, width: 72, bgcolor: #92cddc"]MonthEnd[/TD]
[/TR]
[TR]
[TD="class: xl75, bgcolor: #dce6f1, align: right"]4/6/2001[/TD]
[TD="class: xl75, bgcolor: #dce6f1, align: right"]5/31/2013[/TD]
[/TR]
[TR]
[TD="class: xl75, bgcolor: #dce6f1, align: right"]8/1/2009[/TD]
[TD="class: xl75, bgcolor: #dce6f1, align: right"]5/31/2013[/TD]
[/TR]
</TBODY>[/TABLE]


When i use the formual in excel it works fine for both the data points. However when i use it in powerpivot i get and error for the 1st data point. Any suggestions how i could avoid this error.

Regards,
Ren.