try this:
1. use Notepad open "agent.db" this file

Win7&Vista is in C:\ProgramData\Battle.net\Agent\agent.db
WinXP is in C:\Documents and Settings\All Users\Application Data\Battle.net\Agent\agent.db

2. find http://enGB.patch.battle.net:1119/patch and change to http://enUS.patch.battle.net:1119/patch
* there should be 2 link which is enGB, replace both with enUS.

3. goto program files/Diablo III, find agent.DB and repeat step 2 but in this agent.db only 1 link with enGB

4. after replacing all, save and run diablo 3 like normal then it shall start patching.