According to any of the most knowledgeable Excel users I know you should
consider yourself lucky
Merged cells are one of the most damaging
features ever introduced to the program & the general recommendation is that
they should be avoided under all circumstances. If you're determined to
contend with them...
The only time I've ever seen the option dimmed is when only 1 cell is
selected. If that isn't the problem, the next consideration is whether your
software is current ‹ 12.2.1 for Office, 10.5.8 for OS X. Confirm the update
level, repair disk permissions & restart the Mac. [This information is
always needed before it makes sense to chase any symptoms.]
If the problem persists, is it happening in just the one sheet or does it
happen in any sheet of any workbook? If it's just the one workbook what is
the source of the file ... Did you create it with 2008 or is it a file you
received from another source? If another source, what version of Excel
created it? What is the file format? What other details can you provide?
Regards |:>)
Bob Jones
[MVP] Office:Mac