Hi,

If your roll number is showing invalid when you are using it to download your admit card or when you want to view your results, then please check your documents & the application form whether the number you are entering is the correct one. If there's any other way to do the thing, you can try that too, for example if the registration number works or your DOB. If nothing is working & you are confident about the roll number then please contact the official authorities of the institution, they will be able to definitely help you in this situation.

Hope this helps.