1. Open the registry and find the key below. 

2. Create a string new value and name it 'RasForce', set the value to equal '1' for enabled. 

Key:[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon]
Value Name: RasForce
Data Type: REG_SZ
Data:(0 = disabled, 1 = enabled)
More info: http://support.microsoft.com/support/kb/articles/q172/1/25.asp