This is an all to common problem. I work in a mixed 2003/2007 environment within the office and usually work within compatibility mode saving WB's as XLS instead of XLSX. I use the mround and eomonth functions extensively in my worksheets.
My tip: When I can't get around using them easily, I sometimes put a comment in the first cell with the 'at risk' formula and put the formula text in the comment so I don't have to re-write the whole formula logic again.
I swear this #N/A issue knows when I'm working on a deadline too 'cause that is when it always seems to happen. I'm in hopes that 2010 will not have this issue.
Chris
