I am trying to register my new Pod HD500 and the registration fails with

ESN could not be verified.  Please confirm the supplied USN. ( Error: 523 )

I am entering the serial number (21P5C0Lxxxxxxxxx) in the correct format ((21)XXXNLNNNNNNNNNN, where X stands for number or letter, N stands for NUMBER, and L stands for LETTER) but kep getting the same error.  I can't see a way to raise a ticket online.

Looking at previous threads here some helpful line 6 person usually comes along and regosters the unit to resolve this.

Thanks

Martin