This could happen due to multiple reasons:

1. Invalid PAN card number 

2. PAN has been cancelled

3. Name mismatch 

4. The entered PAN has special characters 

5. The entered PAN is not alphanumeric

If none of the above reasons are valid, give it some time and try again. If the same problem continues, do check on the UIDAI site for more information on your PAN status.