A Volume Shadow Copy Service operation failed. Unknown error (0x800423f0)

I have a pretty freshly installed SBS 2011, which backed up just fine right after I set it up.

After a couple of days, backup stopped working. Whenever I run it, I get the following error:

Backup unsuccessful
A Volume Shadow Copy Service operation failed. Unknown error (0x800423f0)

How can I fix this?

This issue is primarily connected with the installation of the Microsoft SharePoint Foundation 2010 Service Pack 1.

To fix this, perform the following steps:

1. Open an Administrative command prompt.

2. Change directory to C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\BIN

3. Run PSConfig.exe -cmd upgrade -inplace b2b -force -cmd applicationcontent -install -cmd installfeatures