The OPC Foundation has released three major versions of the OPC specification: Versions 1.0, 2.x, and 3.0. The LabVIEW DataSocket API is only compatible with OPC DA Specification versions 1.0 and 2.x. The NI OPC Quick Client, bundled with NI OPC Servers, is compatible with OPC DA Specification versions 1.0, 2.x, and 3.0. If the LabVIEW DataSocket API cannot connect to the OPC server, but NI OPC Quick Client can, the OPC server is most likely operating under the OPC DA Specification Version 3.0.
Some servers allow for the operational OPC DA Specification to be changed while others allow for multiple specifications to be used at the same time. Consult with the documentation of your OPC server to determine what OPC DA specification it is operating under and how to change it.
The LabVIEW Datalogging and Supervisory Control (DSC) Module includes features that allows it to interface with the OPC DA Specification versions 2.x and 3.0 as an OPC client. If changing the specification the server is operating under is not a possibility, consider purchasing the LabVIEW DSC module to interface with OPC servers operating under the OPC DA Specification version 3.0.