If you upgraded to ActiveSync 4.2 and are now having problems connecting to the Internet, a registry key fix might be able to help. According to Microsoft’s Edington Watt, ActiveSync version 4.2 made a change to how it interacts with the Windows networking stack to use Layered Service Providers (LSPs) on outgoing Desktop-Pass-Through connections. This allows for improved compatibility in environments where connections to the internet must be passed through these LSPs (ISA Proxy is one such example). But this change may be causing issues for others. The registry key fix removes this change.
The registry fix and instructions are available at the ‘More information’ link.
Source: Mobinaute