Today I received an email with this link (I stripped out the part of the URL unique to my account). If you go to it and register your Enterprise account #, it appears to give you 20 bonus points for doing nothing, plus qualifies you for double points for upcoming rentals. Give it a try and report if it works for you. Enjoy if it does! http://plusyourpoints.enterprise.com/
The offer appears *not* to be targeted. Perhaps the number you entered was mis-formatted (had an errant space) or incorrect or otherwise problematic - i.e., not rejected because it isn't targeted, but rejected because it is literally invalid? Anyone else get rejected with an account # they are *positive* was entered correctly and is valid?
Same # will let you log into their site? Very odd. Sorry it didn't work out for you - not too many points to miss out on though.