SBS 2011 Backup Failures - A Volume Shadow Copy Service operation failed. Unknown error (0x800423f0)
After some quick research, I found that in some of the updates installed, there was a Sharepoint update that had downloaded, but needed to be manually installed. That's pretty lame, but whatever.
The method of updating Sharepoint properly is discussed here:
In essence, it's just go to an administrative command prompt. Go to this folder:
C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\BIN
and run this command:
PSConfig.exe -cmd upgrade -inplace b2b -force -cmd applicationcontent -install -cmd installfeatures