Error 1720, 1721, or 1723 appears while installing Camtasia.
This error occurs when the installer file is incomplete or corrupt. Download the installation file here. Depending on your system, there may be some other items to consider:
Reason 1: Administrator Login
You may not have Administrator Rights to install software on your computer. Login as an Administrator and then try the install again.
Reason 2: User Account Control (UAC) Blocking Windows Installer
On Windows Vista / 7, the User Account Control (UAC) could be blocking access to the Windows Installer. Disable UAC and then try to install again.
To disable the UAC, click Start Menu > Control Panel > User Accounts > User Accounts > Change User Account Control Settings. Reduce the slider position to Never Notify.