dotnet run throws the error attached in file. I know this function exists, because the official docs say it does. (https://learn.microsoft.com/en-us/dotnet/api/system.reflection.emit.assemblybuilder.definedynamicassembly?source=recommendations&view=net-7.0) Also attached is the full source code with one minor change in XmlRpcProxyGen.cs, in line 105 from AssemblyBuilder assBldr = AppDomain.CurrentDomain.DefineDynamicAssembly(assName, access); to AssemblyBuilder assBldr = AssemblyBuilder.DefineDynamicAssembly(assName, access);, as AppDomain.CurrentDomain no longer holds the function.