I recently had a tough time to resolve this issue.

The problem: The WCF service stopped working without any “breaking” changes done

The exception: The type <xxxxx> provided as the Service attribute value in the ServiceHost directive could not be found. (Complete stack-trace below).

The solution: The class name (aka. type) was missing the complete signature. As my project assembly is strong named and GACed, the declaration should be “type, assembly, version, culturePublicKeyToken”).

 Earlier declaration: <% @ServiceHost Language=C# Debug=”true” Service=”typeXXXXX” %>

The corrected declaration: <% @ServiceHost Language=C# Debug=”true” Service=”typeXXXX, assembly,version=1.0.0.0, culturePublicKeyToken=xxxx” %>