On Mon, 21 Jan 2013 14:14:11 +0000, KeriM wrote:

One sheet (monthly) that has a date written in "mmmm"
format in B4.

What do you mean by this?
Is this a "real date" formatted to display as "mmmm", or is it a text string?

If the latter, then change month(a4) to MONTH(DATEVALUE(A4&" 1, 2012")).

If the former, then post a copy of your workbook to some publically accessible site (e.g. Skydrive) and post a link here so we can see exactly what's going on.