user name

[bigfootsjunkstore]

I attempted to change my user ID but received an error which stated the new user ID was not acceptable.  I followed all the rules necessary to change my user ID but kept getting the same message.  There is no explanation why it was rejected.  What can I do to find out what the problem might  be. I have been am ebay member in good standing for a number of years with 100% positive feedback.  Thanks