You will get an "Invalid License Key" message when you try to enter a licence key in the following conditions:
1) The key entered is in the lower case, or has a space somewhere.
2) You are trying to copy and paste it from your email but it probably has a space before or after the key.
3) If the product installed is wrong / incorrect
4) When the key has expired.
If any of the mentioned conditions do not apply please email us at support@mwti.net