You can copy the llb from Keithley to the LabVIEW\instr.lib folder, this will make it appear in the instrument driver pallette of LabVIEW, LabVIEW reads this directory when it is launched.
As for the error 121, this seems to be generated by the instrument driver, I would advice checking the message string for errors, you should be able to find the correct syntax for these strings in the instruments documentation.
Met vriendelijke groet / Kind regards,
Karsten
Applications Engineer
National Instruments