Excel 2007 : Averageifs Div/0 error when all all cells in numerator range are NA

All cells in the Column Z are NA. The following formula returns a div/0 error.

=AVERAGEIFS('Days Between'!$Z$5:$Z$3100,'Days Between'!$I$5:$I$3100,">=12/01/2011",'Days Between'!$I$5:$I$3100,"<=12/31/2011")

I changed it to an if formula to account for the NA's and it also returned a div/0 error.

=IF('Days Between'!Z5:Z3100<>"NA","NA",AVERAGEIFS('Days Between'!$Z$5:$Z$3100,'Days Between'!$I$5:$I$3100,">=12/01/2011",'Days Between'!$I$5:$I$3100,"<=12/31/2011"))

I want a formula to return NA if all the cells in the range are NA or to average the numbers if some or all of the cells contain numbers.

Help!

Catherine

That works; thanks a million!