I have application workbooks created in Excel 2003 for the individual use of
multiple people. One or two users have Excel 2007, and more may be up
switching (I hesitate to use "upgrading"). There are buttons which process
data and do other things. However not all things work correctly in Excel
2007. Are there known issues, service packs, or references that need to be
added to Excel 2007 to make it backward compatible? Where can I find that
info? Or is it problematic programming?

One issue is that worksheet protection does not turn back on at the end of a
macro after being turned off at the beginning.