How long you had account? Ask adsense support, why you account was disabled, I know adsense support can send email with warning, did you have got any email from adsense team?
for abt 1 month......i placed it in my blog " www.infytime.blogspot.com " didn't receive any warning mails. Only 1 mail i got, which said the account is disabled.
Were you inflating your traffic by redirecting from another URL? There are so many thing Google frowns upon it could be anything. Review their TOS and I am sure you will find the reason.
this is what i got "While going through our records recently, we found that your AdSense account has posed a significant risk to our AdWords advertisers. Since keeping your account in our publisher network may financially damage our advertisers in the future, we've decided to disable your account. Please understand that we consider this a necessary step to protect the interests of both our advertisers and our other AdSense publishers. We realize the inconvenience this may cause you, and we thank you in advance for your understanding and cooperation."
adsense preview tool shows your site is banned as well. if you did nothing wrong then submit an appeal. but chances of getting reinstated in slim to none adsense is getting rid of small publishers who dont earn much and takes forever to reach $100 payout. with your earning of $3.50 in a month, it will take you almost 3 years to get a check. that could be the reason too
In any case, you should not have adbrite ads if they are matchingin scheme and color with adsense ads, nevertheless you generally get a warning for such mistakes and dont get banned outright-this is for some other reason you have been banned