Ineligible for rehire

[053108]

I put my two weeks in at the hospital I worked for about a month or so ago. I was there for 2 years exactly. Well, I gave a resignation letter and followed through with my last two weeks and they deemed me ineligible for rehire. What would be the reason? I was always on time, never left early, done my job, worked great and worked great with others. I missed a week for one surgery last year but it was excused. Can they do this IF i'm the one who resigned? And how will this look when I go for another job? I have emailed HR and have yet to get a response as to why I am ineligible for rehire. I figured I may need to know when I do go back to work. I'm former military and have alot of job experience and have never been deemed ineligible for rehire. I'm really worried as to how this will look on a resume. One thing I should mention is that my first boss was wonderful, we worked great together. Well, we got a new boss and I worked for her the last 7 months, only part time since I am still in school though. Well, I always had the feeling she didn't care too much for me. You know the gut feeling is usually always right. Never said anything though and never gave her reason to not like me. Can she just say I'm not eligible for rehire because of personal feelings towards me?