Are you running an PC optimizer program called "Soluto".. If so, see the link below:

If you're not running the program above, I see the "ActivityMonitor" error showing up in discussions about Kaspersky, Ad-Aware and a few others.. It also shows up in discussions about spyware.. I certainly would download, install, update, and run Malwarebytes and SuperAntispyware to be sure it wasn't malware in nature but since you seem to have already done such, see if you can find the "ActivityMonitor.exe" file on your computer. Maybe the file location, or the file properties will tell you something.

It's easy enough to let the installation proceed by changing the driver signing security to "Allow" the installation.. (Open the "Control Panel", double click on "System", select the "Hardware" tab, then the "Driver Signing" button.. Once there, select the "Ignore" option, then click on OK.) The question is whether you "should" or not. Verify the file and its purpose first.

Hope this helps.