I've noticed quite some people having the problem with the error 740, the error have allready been solved.
The error occurs duo to the servers and client not being same, meaning that, some people like me, have downloaded enUS client not the enEU client triggering the 740 error everytime, that there's an update because your client downloads US patch and you play the EU server.
HOW TO FIX:
Remove Diablo III and reinstall the EU client, by downloading it on Battle.net or w/e, as shown below on the picture:
Steps to fix Error 740:
1. Follow all the steps here first including restart:
2. Go to where your Diablo 3 folder is located. For example: C:\Program Files (x86)\Diablo III
Right click "Properties" for Diablo III.exe then choose the "Compatibility" tab.
3. Under "Privilege Level" Enable "Run this program as an administrator" then click OK.
4. Double click "Diablo III.exe" (It will now update the patch properly)
5. When the update is finished you need to undo the properties changes on Diablo III.exe
Repeat step 2 then Disable "Run this program as an admin".
Once it's disabled again you can now run your regular launcher shortcut or you can double click "Diablo III Launcher.exe"