Error 651 is a well-known bug in Windows 7 which happen when you try to connect to the Internet using PPPoE connection. If you're one of the victims who met this bug, you should see the following error message: Error 651: The Modem (or other connecting device) has reported an error. These connections, however, would work just fine in Windows XP or Windows Vista PCs. Below are a few solutions that can perhaps fix the problem:
Windows 7 Fix: Error 651 Modem PPPoE Broadband Internet Connection
Fix 1: - Error 651 Modem PPPoE Broadband Internet ConnectionClick here to download Registry Easy
to automatically fix your PC errors and speed up your system.
Fix 2: - Error 651 Modem PPPoE Broadband Internet Connection
The root of the problem is believed to be caused by the RAS PPPoE file raspppoe.sys found in the folder C:\Windows\System32\Drivers. To fix this problem, we will have to replace the file raspppoe.sys with a new one. Try to copy the file from your friend's computer which has Windows 7 installed. Alternatively, you can download the raspppoe.sys file from this site (thanks to the author). After you get the file, before pasting it into C:\Windows\System32\Drivers, be sure that you rename the original file to something like raspppoe_ori.sys, so that if something weird happen you have a backup of your original file. Paste the new raspppoe.sys into the directory after you've renamed the original file. Try to connect your modem and it should work fine now.