Ah yes, that problem was fixed in 4.0.3 (or a little before, not sure). 

Since the error is in FindClassesOfType, it looks like something is wrong with your bin folder or something? Maybe permissions.. (yes, they do tend to "magically" change sometimes).

This is the function that fails:

       /// <summary>
        /// Searches all loaded assemblies for classes of the type passed in.
        /// </summary>
        /// <typeparam name="T">The type of object to search for</typeparam>
        /// <param name="useSeperateAppDomain">true if a seperate app domain should be used to query the types. This is safer as it is able to clear memory after loading the types.</param>
        /// <returns>A list of found types</returns>
        public static List<Type> FindClassesOfType<T>(bool useSeperateAppDomain)
        {
            if (useSeperateAppDomain)
            {
                string binFolder = Path.Combine(HttpContext.Current.Request.PhysicalApplicationPath, "bin");
                string[] strTypes = TypeResolver.GetAssignablesFromType<T>(binFolder, "*.dll");

                List<Type> types = new List<Type>();

                foreach (string type in strTypes)
                    types.Add(Type.GetType(type));

                return types;
            }
            else
                return FindClassesOfType(typeof(T));
        }

Line 27 is this line:

                string binFolder = Path.Combine(HttpContext.Current.Request.PhysicalApplicationPath, "bin");

I think you should ask your provider to see if the permissions are still correct and if the whole bin folder actually still exists.