vmax should be larger than vmin error in facetselfcal step

[souley]

Hi all,
I'm trying to run FACTOR on PREFACTORed data from P23Hetdex20. This data is from the observation used for LOFAR SCHOOL 2018 (ObsID 232875) but I only use the first 20 subbands. So, after running through PREFACTOR, there is only 2 merged subbands which are the input to FACTOR. Initially, I was getting "All pixels in the image are blanked" errors in the facetselfcal step of the very first facet, so after skimming through the issues, I thought I may not have enough data for appropriately running FACTOR. But, before trying use more subbands, I tried changing some settings in the parset (I don't recall which ones unfortunately), I managed to pass that error and got into getting "vmax should be larger than vmin" errors from the same facetselfcal step. I tried to determine precisely where in the FACTOR source code the error is coming from. Apparently, from an external library (such as numpy) call inside the make_selfcal_images.py script.
I'm not astronomer, so I try to keep the settings in the parsets as close to defaults as possible. I really appreciate any help in either finding the root cause of the error or using a workaround for the time being.