Browser Blocker allows you to pick and choose which browsers(versions) can access your web page and which ones are given a blocked splash screen.
The link to the plugin page will appear in the "Settings" admin menu. By default the "Simple" options page appears, go ahead and select "enable", then determine what versions of browsers that you would like to block from accessing your website.
Once you have entered in a browser version click the green "+" icon to add it to the list.
After you have added entries for all of the browser versions that you want to block, save the settings and your site will immediately start blocking those browsers.
Browser blocker uses a php based browser detection library, and it does it's best to identify the browser and version that are visiting your site, but sometimes it can give false positives.
If you are receiving this sort of an error, you have 2 courses of action, First you can try clearing your settings and set them afresh to see if that resolves your issue, or you can disable the plugin all together.
If for some reason you have blocked yourself from your website, you can disable the plugin by changing the plugin's folder name in your wordpress plugins directory '/wp-content/plugins/browser-blocker' to be something else '/wp-content/plugins/browser-not-blocker' or something similar, and this will disable the active plugin.
Drop me a line and I will work on getting it added.