Ryan Molden (MSFT) says:
Package.GetGlobalService is relying on at least one MPF package (from the specific version of MPF you are referencing) having been loaded. Since you yourself are an AddIn not a Package you can't guarantee that in any way.
You should pass something like new ServiceProvider((Microsoft.VisualStudio.OLE.Interop.IServiceProvider))) as the argument to ErrorListProvide
Package.GetGlobalService is returning null.
I use this code in my Addin. I test it and I get not error, and I can show errors and warnings in ErrorList Windows VS. I'll testing more for safely.
public partial class Connect
{
ErrorListProvider _errorListProvider = null;
void CreateErrorListProvider()
{
if (_errorListProvider == null)
{
System.IServiceProvider serviceProvider = new ServiceProvider(_applicationObject as Microsoft.VisualStudio.OLE.Interop.IServiceProvider);
_errorListProvider = new ErrorListProvider(serviceProvider);
_errorListProvider.ProviderName = "custom Errors";
_errorListProvider.ProviderGuid = new Guid("xxxxxxxxxxxxxx");
}
}