The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel

[Bluebamboo]

Hi all, I have a windows service application that needs to make request to a remote web service (https:// ...) for uploading files. the contact mechanism between them is a SSL based channel. I assigned my windows service to run under a specified user account and installed the client certificate with that user account as well. And I am getting this exception as title, however, strange enough, I do not get this exception all the time, i got this exception sporadically. Does it prove that I did configure certificate properly? if so, what other reasons would cause this exception??? Any suggestion would be appriciated!! Ming