Harmony throws unknown location exception on Patch

IL Compile Error (unknown location)
   bei HarmonyLib.PatchFunctions.UpdateWrapper(MethodBase original, PatchInfo patchInfo)
   bei HarmonyLib.PatchProcessor.Patch()
   bei HarmonyLib.Harmony.Patch(MethodBase original, HarmonyMethod prefix, HarmonyMethod postfix, HarmonyMethod transpiler, HarmonyMethod finalizer, HarmonyMethod ilmanipulator)