After Updating the Product Key it Cannot Connect to DB.

This section implies that you have the latest .Net Framework installed on your PC.

This is one of the most common mistakes which happens when you upgrade your license to include extra user(s). The information on how many user machines can connect to your Database is embedded in the AdvancePro product key, thus you need to update "AdvancePro Server” to reflect the most recent changes (your new product key).

In order to do so:

Login to AdvancePro on the Server > go to Admin > Utilities > Upgrades and enter new product key there > click Update.