If you can't get to excel to change this option, you should be able to go
through the registry to kill it.
If you're comfortable messing around in the registry:
Windows start button|Run
Regedit (and hit ok)
In xl2002, the registry key is:
HKEY_CURRENT_USER\Software\Microsoft\Office\10.0\Excel\Options
that 10.0 will vary depending on your version of excel)
(look for OPEN, OPEN1, OPEN2, etc.)
These have to be in nice consecutive order. So you might have to rename some to
make them consecutive again (after you delete the offending one).
And since you're working in the registry, make sure you back it up before you
start.
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Another option. Find the addin and move it to a different folder. Excel
shouldn't be able to start and you can turn off tools|addins|SQL Server
Analysis.
(This was a normal addin--not a COM addin, right?)