Met this error when starting Camtasia Studio is just you did not register collectly. Do as follow:
Online check notes (perform prior to installation):
The online check has been updated so that modifying the hosts file no longer works.
Important! delete all hosts that were previously added to bypass the online check, e.g
- 127.0.0.1 activation.cloud.techsmith.com
- 127.0.0.1 oscount.techsmith.com
Block outgoing access to the following IP's in your firewall:
- 157.56.8.159 (hostname: activation.cloud.techsmith.com)
- 69.167.144.18 (hostname: oscount.techsmith.com)
Do not un-block them since the application continuously tries to access them to validate the activation code. Alternatively, If you do not wish to use the online features of the application, you can completely block the application in your firewall.
When you succeed, you will see this prompt instead:

BTW, another choice is to use the portable version, which you can find it here:
TechSmith Camtasia Studio v8.x Portable Full for Windows