Trouble getting my Ox to work..

Hi, I am nearing the end of my 500 x 750 Ox build. everything went well until it came time to get the electronics working. I couldn't get the end stops to work at first, but eventually found the correct $$ setting in GRBL. Now when I try to do anything Universal g code sender goes into an error state and I have to use Windows task manager to close the program. I am using Arduino Uno with Protoneer CNC shield and standalone stepper drivers. I have tried several solutions found on the internet to no avail ( some of them I couldn't even understand) I am now at my wits ens and have a very expensive doorstop. Attached is a screenshot of the problem...Attachment 25794 Attachment 25794