When using direct connect to an Oracle database on a 64-bit server and attempting to publish an .mxd, an error message is encountered:
"Server Object instance creation failed - server library cannot be loaded"
When connecting to an ArcSDE service the .mxd can be published successfully.
This issue can occur if the Oracle 32-bit client is not installed on the server. ArcGIS Server 9.x and 10.0 are 32-bit applications and require the use of the Oracle 32-bit client for direct connections.