Database backup, Data recovery et al

In discussion with Microsoft OS support escalation engineers during a SQLServerFAQ meeting one of them revealed that the most common issue that is raised with them is when a system rolls or refused to install back a service pack or patch or hotfix.

So why do some systems stubbornly refuse to upgrade or accept service packs? If at some time in the past the system drive became full and a well meaning engineer cleared off "unused" or old files then, this could be the smoking gun. The major reason for service packs failing or rolling back was the deletion or loss of MSP files. And a frequent cause of their deletion was freeing space on full system drives. A missing MSP file will cause subsequent patches which refer to this file to fail and roll back. It is difficult to copy these files from other systems as they are given a GUID name when when are created by the msi install process. The most straight forward solution is a complete reinstall. So the moral is: don't delete or let anyone delete *.msp files! They don't stop your system working but they do stop upgrades!