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I was having trouble getting ActiveSync 4.5.0 to work on my internal LAN with my Windows Mobile 6 device. It worked fine from the external/Internet. The error reported by ActiveSync was, “The server could not be reached. This can be caused by temporary network conditions. Support code:80072ee2.” With the help of this thread, I was able to easily resolve my problem.

First, I needed to install the PHM Registry Editor, which wasn’t as seamless as most WM application installations are. PHM Registry Editor is pretty old and doesn’t work with the latest ActiveSync. I had to copy the proper cab file (found in %ProgramFiles%\PHM\PHM Registry Editor) to the device and install that way – it was trial and error to determine which cab file was the correct one.

I then used the tool to change the value of:
HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\InternetSettings\DnsCacheEnabled
to 0 (If DnsCacheEnabled does not exist, create it as a DWORD value).

After a soft reset of the device and it didn’t care which network it was on.

Here are the details from the thread regarding what the actual problem was and why the method above corrected it:

Symptom:
– ActiveSync DirectPush initially works correctly wirelessly.
– The Windows Mobile device is then connected to a PC via USB and
continues to operate correctly.
– Once the device has been disconnected, wireless synchronization
fails. ActiveSync times out and clicking “View Status” reveals a status
code of 0x80072EE2.
The device then refuses to sync wirelessly until a soft reset is
performed.

Further Details:
This problem is seen in configurations where the Exchange server being
accessed for synchronization has different external (i.e. public) and
internal (i.e. private) IP addresses which are normally resolved from
the same FQDN. (e.g. On the Internet echxg.foobar.com might equate to
99.88.77.66 while on the inside of a NATed network with an internal DNS
it might equate to 10.9.8.7.)

Cause:
The issue appears to have to do with the Windows Mobile DNS cache not
being cleared properly upon a wired/wireless state transition when the
USB cable is unplugged. When connected to a PC running the desktop
ActiveSync software a Windows Mobile device has proxied wired access to
the corporate network and performs a DNS lookup of the Exchange
server’s FQDN against the internal DNS. This address appears, however,
to remain in the cache even after disconnecting the USB cable and thus
moving back to the public (internet) address space. ActiveSync on the
Windows Mobile device then fails, as the server’s internal address is
inaccessible. (A soft reset naturally clears the DNS cache.)

Workaround:
Disable the Windows Mobile DNS cache. This requires a registry
modification. Windows Mobile does not include a registry editor, but
free third-party editors are available (such as one from www.phm.lu).

Change the value of:
HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\InternetSettings\DnsCacheEnabled
to 0
If DnsCacheEnable does not exist, create it as a DWORD value.

A soft reset is necessary for the change to take effect.