Hi Arthur,
If you put the pins in the wrong way around, the head of the pin sticks out and may cause damage to skirtings etc. When put in correctly (see pic, should be inserted from this side) the head of the pin is below the surface. Make sure the ball catches are working ok at the other end of the pin.
If the machine is jamming, check the bearings for free movement. These are located at the side where the pic was taken. At the other end of the machine is where the drive gears are situated and are accesible when the cover is taken off, you can also check these.
If you need to change the bearings, they are about £10 a pair from Envirodri. I can also let you know the easyest way to change them.
John