Yes. The CAT form may be rejected by IIM depending on the kind of mistake you have made. In case the mistake is editable in the correction window, you can do that. But if the mistake is not editable and you have not even corrected it by filling a fresh form before the last date of CAT registration, IIM has the complete authority to reject the CAT Application Form. Therefore, the candidates must be very careful while filling out the CAT form and should follow the instructions point to point to avoid getting the form rejected.