If you're using certificates to authenticate, and you get the above error, then the root cause may be this:

System.ServiceModel.Security.MessageSecurityException
The security timestamp is invalid because its creation time ('2008-10-02T02:50:25.161Z') is in the future. Current time is '2008-10-02T02:44:44.909Z' and allowed clock skew is '00:05:00'.

Basically, if your client and server have clocks that are different by more than 5 minutes, the timestamp that they send to each other when they authenticate may be more than the tolerance allowed (default 5 minutes).... and it will fail.

The solution is to change one of the clocks :)

Kirk