Error 1911 can occured when installing Checklan Central Admin or Checklan Alerter.
An installation error is generated, explaining that an Ocx or Dll is system protected and can not be replaced or updated.

Select Ignore and continue the installation process that will be successful, it just means that the right file is already installed and is used by the system during your setup or can not be registered. This has no effect on the setup process and the file is installed.