Authorities in Texas say Mike Tyson properly registered as a sex offender with police in San Antonio when he trained there briefly last year.
However, his name doesn't appear on the state registry of sex offenders.
Tyson has applied for a licence to box in Texas in order to fight Lennox Lewis.
State law requires people convicted of sex crimes living in Texas or just visiting to register with authorities. Tyson was convicted in Indiana in 1992 of one count of rape and two counts of deviate sexual conduct.
Tyson attorney Darrow Soll of Phoenix said he went with Tyson to register with San Antonio police on March 30, adding: "I can only tell you that any assertion that Mike didn't register is ridiculous.
"Mike always registers. Mike always tries to fulfill his obligations."
Police spokesman Gabriel Trevino confirmed Tyson registered with local authorities and notified them when he left about two weeks later.
He commented: "As far as the San Antonio Police Department is concerned, he complied with the law.
"Whether or not there was an administrative breakdown, that's not Mike Tyson's fault."
Tyson's paperwork was supposed to be sent to the state Department of Public Safety, but it never arrived.