This error can occur for a couple of reasons. First, if you're trying to install AdBlock on a managed computer, such as at a school or your workplace, your systems administrator may be preventing installation of additional software. You'll need to ask them to install AdBlock for you.
If this is your own computer, you may be signed in on an account that doesn't have administrative rights. Do you get the same error if you sign in with an administrator account and then try to install AdBlock?
Last but not least, malware on your computer can prevent installing software that might try to remove it, such as ad blockers and antivirus/anti-malware programs. Just to be safe, we recommend that you scan your computer with an anti-malware program. We like Malwarebytes Anti-Malware Free. We're not affiliated with them in any way; we've just found that their software tends to find malware that others miss. Also, it's free. :)
If none of these suggestions helps, please try these troubleshooting steps, proceeding to the next step only if the previous one didn't resolve the issue:
- Clear your browser cache and cookies and restart your browser.
- Restart your computer.
- Go through your browser's recommended troubleshooting steps: