TigerWeb(formerly Banner) will not let me register, why?

One reason could be that you have a Hold or Holds on your file. You may owe the school money. You may need to submit paperwork. Perhaps transfer credits from another college are not recognized by the student's self-serve account. Maybe the class you are trying to register for has a prerequisite or requires that you make a certain grade on a test from a previous class. What ever the reason above you need to check with your advisor.