This error may appear when activating offline certificate.
Error: Invalid client date
Solution: One of the things included in the offline activation request is a timestamp from the client. The "Invalid client date" error indicates that the server has determined that the client data (timestamp) is invalid. The most likely cause is that the client's system time is incorrect and needs to be set.
In our experience a somewhat common problem is that the client time is correct but the date and/or year is incorrect. Often when you ask an end user to verify the time, they look only at the time and forget to check the date.