Course Search & Enroll - "You are not able to drop your last class for the term" Error
What it means
Once the semester starts (12 a.m. on the first day of the classes' sessions), you cannot cancel your enrollment by dropping all of your classes.
What to do
Submit a term withdrawal.
For more information and a step-by-step guide to withdrawing from the term, see Student Center - Withdrawing from a Term.