Nant build fails due to registry error for .net 3.5 location

I had a problem that the build wouldn't run and was producing the following error

"The SDK for the 'net-3.5' framework is not available or not configured."

I narrowed this down to Nant not having the right location for the .Net 3.5 SDK, below is a great article which describes the problem in full.

http://www.timbarcz.com/blog/NantSetupForVisualStudio2008AndNet35.aspx