League of Legends
If your patcher logs show many lines like this:
RADS::Common::HTTPConnection::GetFile: File not found
And that happens with files with a name similar to this:
The cause is that your provider is blocking any URLs that contain any pornographic content. Apparently that includes cases like this. An other cause are Router protection settings, which may also block the word sex.
If you are experiencing this problem, you can try to get the whole LoL folder zipped from a friend every time you patch, or just call your ISP to lift the blockade.
Edit: This should only happen to people who switch or signup with new ISPs after a certain date (I'm assuming 1st Jan). The filter won't be on by default to any existing customers, at least it won't on BT, so most people will be unaffected. If the filter is on, all it takes is a call to your ISP and it's off. (thanks to /u/mejti )