Measure Tool Not working

[NoelWilson]

Ihave had several of my editors tell me that occasionally the Measure Tool on the Standard Toolbar is grayed out and not accessible.  There is no rhyme or reason as to when it occurs.  Has anyone else had this issue?  I have installed up to SP 2 for ArcMap 10.

[BarryNelson1]

Check the coordinate properties in the data frame. There is possibly none assigned. I had this issue and that was the fix for it.