Jamming Risograph MZ 770e paper feed problem

This has not been my week however, this forum is great. I posted a problem yesterday and already have had
a very helpful reply.
I now have a new problem. Paper does not leave the machine properly - two sheets together come out about half way
and then machine stops showing error code J2.
I have blown away any dust I could see around sensors etc but does not help. I can hear a slight whinning noise - not much but,
was not there before. The machine has new feed tires (tyres) and they are fitted correctly.
Any suggestions wiull be much appreciated.
Thank you