Update version numbering 12.1.0 and 12.0.1 are apparently confusing some users trying to update to Office for Mac SP1 via Mactopia Downloads.
If you receive this error, be sure you have downloaded the correct updater.
You cannot install Microsoft Office 2008 for Mac 12.0.1 Update on this volume. A version of the software required to install this update was not found on this volume.
All will be fine if you make sure that you download this file: (this is English version name)
File Name: Office2008-1210UpdateEN.dmg
Version: 12.1.0
Date Published: 5/13/2008
If you have downloaded the correct version and get a similar error indicating "there was nothing to update" see Workaround when Updater fails.
Also see Failure to Update Office 2008 Added June 9, 2008

Comments (5)
"All will be fine" ? No it will not ;(
I tried reinstalling office after removing it, no luck.
Even tried the English version in stead of the Dutch one, which
is the one I want.
Still get "A version of the software required to install this update was not found on this volume.".
Are there any other solutions?
This is just one fix for the 'version not found' problem. As outlined in the post, it's possible you downloaded the wrong file. Did you click on the link for the workaround?
Workaround for version not found
There were previous problems that involved the Dutch version. I'll contact you off list with some questions that I can forward to the developers if the workaround does not work for you.
I have tried to use the workaround for the english version to no avail. SP1 will simply not install. Please forward this issue to the developers, as it is upsetting not to be able to install a "critical update."
I'll contact you personally to see if we can help find a solution.
If a solution was found for this please post it.
I have run into this same situation on about half a dozen of my clients' machines. It's really frustrating. Sometimes the "workaround" works and other times it doesn't.