When running a job with spot colors, a "LibScreenParams" error is generated only when running jobs with one or more spot colors.
When running a file through Nexus, a "LibScreenParams" error is generated when the job tries to rip a spot color. The job runs through completely if the calibration is turned off or the file only contains process colors.
One possible reason for this error is due to the SymphonyCalibrator curve used in the Raster Separation module. Open the calibration file used and make sure that a default curve is included in the calibration besides the typical CMYK curves.