Which version of Errai and Weld are you using? Our JettyLauncher shouldn't be required anymore for running your Errai CDI apps in DevMode (in Errai 2.4 and 3.0).
Can you try without it to see if that works for you and post the error here in case it doesn't?
Hi Christian, thanks, I wasn't aware that the jetty launcher was no longer required. Removed it from the project now, it's working perfectly. No errors! Many thanks!