(I hope this helps someone avoid the 24 hours of pain I've just been
through!)

I manage a 2003 Server in a different country via Terminal Services.
The only software on the box is Office 2003 and Adobe PDF. For
months, we've been having the dreaded 'Cannot use object linking and
embedding' error whenever someone opens an Excel spreadsheet; when
it's being opened interactively, no problem, you just hit cancel.
However, when it's opened via a macro (of which we have dozens), no
dice, the macros fail. Even when run as an administrator.

When you google for "Cannot use object linking and embedding", most
solutions are along the lines of "it's the MS Blaster worm". Well, I
ran the anti-virus tools many times, it wasn't that. Another
suggestion was incorrect settings in DCOM config. Nope, they checked
out. Another suggestion was 'reboot into safe mode, open Excel, close
it, then reboot into normal mode' - strange, but fine, I'll try it -
except I'm thousands of miles away from the machine, and our hosting
is very poor, it just wasn't an option (if there's a way of booting
into safe mode and still being able to get in via TS, I'd be very
interested to hear it - I played around with the boot.ini on my local
VMWare copy of the server, and I couldn't see how it could be done).

Now, there has always been one account unaffected by the error, a
particular Power User account, and we had no idea why.

Anyway, I re-installed Office, and latest updates. Nope, problem
still there, except for this one account. For the thousandth time, I
checked out the DCOM settings. Nope, all ok... hang on.. what's
this? Five entries below "Microsoft Excel Application", there's
"Microsoft Office Excel 2007 Workbook". Not seen that before, we
don't have Excel 2007, it's never been installed on the server. Lo
and behold, under this entry, Excel is set to run as the Power User
that never had the problem. Which would imply that the DCOM config
entry I'd been checking all along is redundant; which isn't the case,
as I've made changes and seen the results!

So, I set the 'Microsoft Office Excel 2007 Workbook' AND 'Microsoft
Excel Application' DCOM entries to the same (desired) settings, and
everything works fine again - macros run, users are happy.

If I hadn't just spent so many hours on this one issue, I'd try and
track down exactly where the rogue 2007 entry came from, and why
changes to BOTH entries affect Excel. (I have my suspicions that an
MS Update may be responsible; I manage another, completely unrelated,
server and have experienced much weirdness directly after an MS
update.)

Like I said, hope this helps someone at some point in time!

Regards,

Nate