Error

System.InvalidOperationException: Unable to generate a temporary class (result=1).
error CS2001: Source file 'C:\Windows\TEMP\beo4ycyh.0.cs' could not be found
error CS2008: No inputs specified

   at System.Xml.Serialization.Compiler.Compile(Assembly parent, String ns, XmlSerializerCompilerParameters xmlParameters, Evidence evidence)
   at System.Xml.Serialization.TempAssembly.GenerateAssembly(XmlMapping[] xmlMappings, Type[] types, String defaultNamespace, Evidence evidence, XmlSerializerCompilerParameters parameters, Assembly assembly, Hashtable assemblies)
   at System.Xml.Serialization.TempAssembly..ctor(XmlMapping[] xmlMappings, Type[] types, String defaultNamespace, String location, Evidence evidence)
   at System.Xml.Serialization.XmlSerializer.FromMappings(XmlMapping[] mappings, Type type)
   at System.Web.Services.Protocols.XmlReturn.GetInitializers(LogicalMethodInfo[] methodInfos)
   at System.Web.Services.Protocols.HttpServerType..ctor(Type type)
   at System.Web.Services.Protocols.HttpServerProtocol.Initialize()
   at System.Web.Services.Protocols.ServerProtocolFactory.Create(Type type, HttpContext context, HttpRequest request, HttpResponse response, Boolean& abortProcessing)

Solution

After adding the application pool service account to the local administrators group, this error was resolved.

We are now looking into a real solution