Just my personal experience with Avast free 7.0.1474 on a Windows 7 netbook.
This was a Google Chrome related issue for me. The Avast WebRep crash "balloon" originally started appearing about a week ago when I would attempt to launch a Windows 7 msn.com weather module on my desktop. (The module was associated to launch Chrome.) When I tried to load other urls directly in Chrome the same Avast WebRep error would pop up.
Attempting repair of Avast in Control Panel did not work and no repair option was available for Chrome in Control Panel. Since Chrome was crashing trying to load all other websites anyway (I would get a "Snap" crash page), I just uninstalled Chrome altogether. I have not had an issue with Avast WebRep error appearing since.
Upon uninstalling Chrome I was asked which default browser I wanted to revert to. I selected Firefox 16.02, a browser I know to work well on my machine. No further issues. I did not have to uninstall/reinstall/change settings in Avast at any point.
I don't understand the connection between Chrome and the Avast WebRep error, I only know the issue was resolved by taking Chrome out of the picture.
Jefferson Santiagos advice above may work, as well, but I did not find it soon enough to try it.
I did check Avast->Additional Protection->Browser protection->Settings->Plugins, as he mentioned, and noticed that WebRep protection is still showing as active for my other two browsers, Firefox and IE, both without issue. My weather module is even working again!
There is an option on the Avast Settings menu to disable WebRep. I suppose one could deselect that and the protection would be removed, presumably eliminating the error balloon, without having to uninstall Chrome. It's worth a try. I prefer to keep it enabled and just associate different browsers with it.
I wasn't using Chrome as my main browser anyway so I don't miss it or the aggravation of a crashing WebRep and websites.