Hi Joyce,
Thanks for reporting the problem!
Good news -- we found the error that caused this we have just fixed the issue, so you should be able to reactivate your Little Math successfully now.
Please try doing the following:
1. Open Little Math (you will find that it is still deactivated.)
2. Re-import your license key
3. Your Little Math will be activated and working as per normal.
We sincerely apologize for this inconvenience, and we thank you for your understanding and support.