HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchangeOWA\AllowInternalUntrustedCerts = 1
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchangeOWA\AllowExternalUntrustedCerts = 1

If applied to the Exchange Server 2007/2010 will help.
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= Taym =
MK2a #040103216 * 100Gb *All/Colors* Radio * 3.0a11 * Hijack = taympeg