Re-install Combo Update 10.6.7 says volume not available

Thanks so much for that info I no the machine was updated in software update, but now can't remember if it was definitely delta or combo - I can confirm that the iMac's current build is: 10J4138.

Thanks for your support.

After some exploring, I see that there is a download available for a "custom" OS X10.6.7 Update, specific for 2011 iMacs. It was just released this month.

Mac OS X 10.6.7 Update for iMac (early 2011) 1.0.

They don't give the build number for it, but it may have been what you recently installed as a software update. In any event, your current OS build is apparently later than the build of the "standard" 10.6.7 Combo update - that update is dated March 2011, and is presumably build 10J869. It is not surprising that the older Combo updater won't install over your current newer build, even though they are both labeled 10.6.7. You might be able to download and reinstall the new "custom" 10.6.7 iMac updater from the above link, should you care to do so.

Thanks for the sleuthing. AFAICT, there's no COMBO version, which makes sense, since it's only updating the specific build shipped with the new machines.