I have opened a ticket for you on these issues so we can look into them further. For the repeat activation this problem can occur if you have a dynamic or changing MAC address on your machine. I have posted some steps you can take to record these values to determine if this is the problem for your activation.
As for the other issue with the cart this sounds like an issue that should be fixed in the latest release of eCart 4.5.2 at the time of this post. To update your ticket please login and visit your support history.