I never have and don't ever plan on trying to create a network link between two building using buried ethernet due to potential grounding issues.  I don't personally have any issues dealing with it but have heard horror stories of switchgear mysteriously failing between buildings.  I generally don't like to blame equipment or wiring because too often problems arise from configuration changes or a change somewhere in the system but if the switch works in a different location I'd venture that you probably do have a wiring or grounding issue.  My suggestion would be to pull a fibre line through your conduit or setup a wireless link.