There is a known issue within the gencal task that when attempting to create Tsys calibration tables for WSRT data it will result in the error messages:
SEVERE Calibrater Caught Exception: SYSCAL table is incomplete. Cannot proceed.
SEVERE Exception Reported
SEVERE gencal An error occurred running task gencal.
This occurs because gencal was developed with the calibration of ALMA Tsys data specifically in mind. ALMA Tsys data is measured and recorded as a spectrum which is filled into the SYSCAL table of the measurement set (MS) upon importing from the ASDM format. Because WSRT Tsys data is unchannelized the importation from UV FITS does not fill the SYSCAL table in the way gencal is expecting.
If the WSRT Tsys data is originally stored as a UV FITS TY table then it may be possible to ingest that data into the MS but it would likely require further tweaking to get the gencal task to work properly on it. There are no plans for the CASA project to address this WSRT data-compatibility problem.