Originally Posted by texaskid

It just means that it doesn't follow the old SSN format where the first 3 numbers were "area codes", followed by so-called "group numbers", then your personal number. However there were rules about which area codes and group numbers were supposed to be used together. The whole system was randomized in 2011, because some areas were running out of available numbers.
I had the same problem back in the day, because even though mine was issued in TX, it starts with 009, which was originally used in Vermont, but the assigned group numbers were never used there, so I was getting the unable to validate number errors. That's basically how they were able to filter out fraudulent/made-up numbers before 2011