The following errors may occur when sharing an Internet connection in Windows 7:
An error occurred while Internet Connection Sharing we being enabled.Internet Connection Sharing cannot be enabled. A LAN connection is already configured with the IP address that is required for automatic IP addressing.
This can be fixed with the following two commands:
netsh int ip reset
netsh winsock reset catalog
After executing these two commands with administrator privileges, restart and you should be able to share your Internet connection normally.