Some people have run into difficulties using ActiveSync 4.0.
Everyone who uses a Windows Mobile 5.0 handheld or smartphone has to use ActiveSync 4.0, as this operating system will only work with the latest version of this synchronization software.
Unfortunately, some devices are having connection problems using ActiveSync 4.0.
According to Microsoft, these are "caused by interoperability with desktop firewall applications or applications that manage network traffic. These applications appear to conflict with the TCP traffic between a Device and the PC."
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