6210 - display shows "SIM error STOP"??

I have a 6210 which comes up with "SIM error STOP". I have tried known
good sim cards from all 4 networks. I have also run Eeprom Tools v4
and the 6210 passes all Start Up Self Tests - so I think the eeprom is
not corrupt.

With no sim installed , the 6210 comes up with "Insert Sim" , as
expected.

I have searched the net and not found any mention of the above
problem.

Maybe I need to reflash the 6210 with good firmware? Or maybe its a
hardware problem. I've taken a look inside and there is no obvious
problem. However , the LCD is missing one horizontal line at the top
of the display - but I don't think this should effect operation.

Any thoughts on why I get "SIM error STOP"?

Thanks