MyHP psc 1350 all-in-one printer keeps refusing to print envelopes - I've made sure that they are loaded correctly but the printer just keeps jamming them up! I've searched the instruction manual for help but it doesn't have a section on unjamming - I've had to pull the envelopes out which I'm scared may damage the printer. It works fine on ordinary paper. Does anyone have any ideas how to rectify this problem please. Thanks.