!040 rejection

For the second year, my electronic filing has been rejected three times by the IRS.  Each time, the obstacle is my EIN number.  It is correct--that is, it is the number given to me by the IRS a few decades ago.  I check and re-check it.  I re-type it in the files.  Nothing works.  Does anyone have a suggestion as what I should try to do to circumvent the problem?  I can of course file by mail.  I would prefer not to.