The problem was that the ID column wasn’t getting any value. I saw on @Martin Smith SQL Fiddle that he declared the ID column with DEFAULT newid and I didn’t..
MSDN Documentation Here
To add a bit of context to M.Ali’s Answer you can convert a string to a uniqueidentifier using the following code
SELECT CONVERT(uniqueidentifier,’DF215E10-8BD4-4401-B2DC-99BB03135F2E’)
If that doesn’t work check to make sure you have entered a valid GUID