You are receiving error 1720, 1721, 1723 while installing Camtasia.
This error can occur for several reasons but is usually the result of an incomplete or corrupt installer file. Please try downloading the file again via the TechSmith Free Trials webpage.
Depending on your system, there may be some other items to consider:
You may not have Administrator Rights to install software on your computer. Login as an Administrator and then try the install again.
On Windows Vista / 7, User Account Control could be blocking access to the Windows Installer. Disable UAC and then try the install again.
To disable the UAC (User Account Control) go to Start > Control Panel > User Accounts > User Accounts > Change User Account Control Settings and reduce the slider position to Never Notify: