Just in case this works: I found this post from K9 Web Protection's facebook page and I will be trying it out.
I will report back if it works for me:
It appears that an update to Avast Antivirus is causing a conflict with K9. If you have Avast and K9 installed, and are having problems connecting to the Internet, please try the following steps:
1. Go to the Avast Console.
2. Click on [Real-Time Shields].
3. Next Click on [Web Shield].
4. Click on [Expert Settings] and then [Exclusions].
5. Next add "k9filter.exe" (without the quotation marks) to the "Processes to Exclude" list.
6. Click [OK]
You may need to wait a minute for the setting to take effect, but it should resolve your issue. If you have some other antivirus installed, or are having other issues with K9, please contact our support team at
http://www1.k9webprotection.com/support/contact - and we'll get back to you as soon as we can.