Thank you for your question. I look forward to working with you to provide you the information you are seeking.
The violation you were denied entry over is a documentation violation. The reason you were inadmissible is as follows (directly from the statute): (i) In general.-Except as otherwise specifically provided in this Act, any immigrant at the time of application for admission- (I) who is not in possession of a valid unexpired immigrant visa, reentry permit, border crossing identification card, or other valid entry document required by this Act, and a valid unexpired passport, or other suitable travel document, or document of identity and nationality if such document is required under the regulations issued by the Attorney General under section 211(a)
Thus, it seems you were not allowed entry because you did not have proper documentation, at least according to the rule they stated for denying you entry (all I know is what you told us).
If you are a Canadian citizen, you do not need anything but a proper Canadian passport that is not expired for entry into the US. Of course, it seems too that you may have exceeded the 6 month maximum stay in the US in any 12 month period, which means you have to wait 12 months since you last left the US and if you last left the US in April 2012, then you should be admissible again without any issues.
Thank you so much for using JustAnswer.com. I truly aim to please you as a customer, but please keep in mind that I do not know what you already know or don't know, or with what you need help, unless you tell me. If I did not answer the question you thought you were asking, please respond with the specific question you wanted answered. PLEASE use REPLY to EXPERT if you would like more information or if you feel something was not included in your answer.
Kindly remember the ONLY WAY experts receive any credit at all for spending time with customers is if you click on OK, GOOD or EXCELLENT SERVICE even though you have made a deposit or are a subscription customer. YOU MUST COMPLETE THE RATING FOR THE EXPERT TO RECEIVE ANY CREDIT, if not the site keeps your money on deposit.
Also remember, sometimes the law does not support what we want it to support, but that is not the fault of the person answering the question, so please be courteous.