C3760dn Duplex causing paper jams 050-011

My Dell c3760dn has started jamming every time I use the duplex printing. It jams as it takes the paper back into print the other side. I have dismantled what i can and cleaned/ checked for anything obstructing the path. Also ran the CE mode tests which seemed to be ok.

I get the error 050-011 when the jam occurs. Otherwise the printer works absolutely fine.

Any advice would be appreciated as dell technical support line don't want to help!!