Lane Garrison -- I Didn't Hurt My Ex-Girlfriend

Lane Garrison says he did NOT hurt his ex-girlfriend Saturday afternoon ... but he's spending the night in jail because he's on a parole hold.

Garrison's lawyer, Harland Braun, just met with Garrison at the Beverly Hills jail. Braun says Garrison and GF Ashley Mattingly had broken up, but Garrison made a bad decision -- he went to her Beverly Hills apartment building to dog sit for his acting coach, who lives on the 3rd floor.

Garrison left the apartment unit and went downstairs to leave, but ran into Ashley in the lobby. Braun says Garrison told him ... the two began arguing about the failed relationship, and Ashley started screaming and threw Lane's cell phone against the wall. Braun says Lane then put his hands on Ashley's shoulders, put her in a chair, and then left. Lane says he did not harm Ashley.

Now get this. Lane -- who did prison time for crashing a car that killed a high school student -- is 6 days away from ending his parole. Braun says Ashley knew this and it could be her motivation for getting Lane arrested.

Braun says Ashley's injuries could have been self-inflicted.

The stakes are high for Lane. He was arrested for felony domestic violence and if the case sticks ... he could go back to prison in the manslaughter case as well as the domestic violence case.

Lane says he wants to stay in jail tonight so he can speak with detectives as soon as they come in Monday AM.