For EQMOD I will provide a COMException to report an InvalidOperationError using the error code 0x8004040B - however I suspect that EQMOD may be the only driver doing this and other drivers may well apply their own “unique” sets of errors codes (the meade driver for instance uses 0x8004040B to report a “below the horizon” specific failure)
So it maybe that a more generic/pragmatic solution is simply to trap the COMException and, irrespective of the associated error number, just take this as an indication that the requested function has failed.
Chris S.