Unable to run website that uses Microsoft.Crm.Sdk.dll after CRM 2011 upgrade

I was getting the following error when loading a website that used the Microsoft.Crm.Sdk dll (CRM 2011). The error started occurring right after I installed CRM 2011.

System.IO.FileLoadException: Could not load file or assembly 'Microsoft.Crm.Sdk, Version=5.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)
File name: 'Microsoft.Crm.Sdk, Version=5.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' ---> System.IO.FileLoadException: Could not load file or assembly 'Microsoft.Crm.Sdk, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)
File name: 'Microsoft.Crm.Sdk, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35'

Luckily for me, CRM 2011 Update Rollup 6 was available. Installing this rollup and then restarting the CRM server fixed the issue for me.

If you need a manual fix, please check David Jennaway’s post: http://mscrmuk.blogspot.com/2011/02/using-crm-40-assemblies-on-crm-2011.html