When I log on the internet this pop-up shows up.

You may have downloaded an Internet Explorer Toolbar, and it is not working properly.

It's called MyWebSearch, you might see it just under the address bar on Internet Explorer

Double Click Programs and Features icon in the Control Panel (in Classic View) and Uninstall MyWebSearch.

Also, in Control Panel, double click on Internet Options. Then click the Programs Tab at the top of the box that opens. Then click the Manage Add-Ons button.

Look for MyWebSearch in the list in the Window that pops up and disable it by left clicking on MyWebSearch to highlight it then clicking the Disable button below the list.

Hope this helps, let me know if it fixes the error.