Phaser 6121 paper size problem

Hello,

i have a strange problem with phaser 6121mfp

When a print (from any pc) the page will be printed, but i  receive an error "paper size problem" if i confirm, the printer we will back online. I check configuration and driver and everything is correct.

I also try to clean loader roller, but nothing change.

Anyone have some idea?

thanks for reply.

best greetings

Alex