‘ScriptManager’ is ambiguous in the namespace ‘System.Web.UI’

I ran into an odd programming problem today, but as usual google came to the rescue.

I am linking to the blog that had the solution.

"Well, that was the end, as it turns out I had installed both the Ajax that comes with the .NET 3.5 and the Ajax that comes with ASP.NET 3.5 Extensions, and I had referenced them both! All I needed to do was to remove one of the references and that’s it."
Solution