Priport JP 5000 only first print jam

[zoran.riko]

When making new master, ONLY first print is jamed at B position. After removing jamed sheet, prints at all speeds and quantity without any problem.
Can be problem with paper registration or feed timing or clamping at specific speed ?
Which speed is using when making first print?

[albasoul06]

JAM FEED IN [feed in jams only during proof / start up] - registration sensor
JAM FEED IN [feed in jams only during proof / start up] - rom C231 5107D, C231MP1D.exe- TSB C231-006

Start up or proof copy jam [jams at start up or proof copy] - replace MPU
Start up or proof copy jam [jams at start up or proof copy] - set SP mode 6-112-1 to 34 default