I notice you're using GMCP, which is generally an IRE thing. Mudlet has an IRE mapping script already and it is kept up-to-date with lots of useful functionalities. You can view it here.
In answer to your question, you can display errors by clicking on the Errors or Debug window within the Mudlet editor.
I'm not too familiar with GMCP, but I think the event handler would be gmcp.Room.Info, with the caps.