Can't Activate Paid License in Demo Mode

On a Windows XP SP3 system, I have eM Client installed and it’s in “Demonstration mode.” After paying for a license, I clicked the “Activate” button, copy/paste my activation key, and click the OK button.

Next to the Activation button, I see the rotating dots as it’s working, but then it stops and I’m back to the dialog in Demonstration mode again.

How do I get my license to work? (Dennis.Hays [at] haysdesign [dot] com)

there was no error message at all?
If not please check your firewall and antivirus settings, whether emclient
can access and on port 80.
If this does not help, please enable network communication logging (tools -> Settings -> Logging -> Network communication), restart eM Client, repeat the activation process and then send us logs (send logs button on the same page of the settings).

Have you seen the log and does it say anything?