Array dimension error

[FCarotenuto]

Dear all,

I'm running ATCOR4 and testing different correction routines for some airborne images (e.g.: running ATCOR4 flat terrain, vs. ATCOR4 with DEM and other options). 

Sometimes, apparently randomly, while ATCOR4 is computing the Atmospheric Correction (after having clicked on "RUN Atmospheric correction", after having updated visibility for excessive negative reflectance pixels), it suddenly stops with this IDL Error:

">>> constant0_atm_4r-Error <<<
---------------------------------
Array dimensions must be greater than 0."


I can't understand what's causing it. Sometimes it simply solved by restarting the computer, sometimes it is enough to re-prepare all the DEM files from scratch and repeating the procedure, sometimes, as in this moment, I can't seem to solve it and keeps crashing all my attempts at running the atmospheric correction. 

In attachment there's the log for the atmospheric correction procedure. It mentions the error happening while running APDA1_LUT_CONSTVIS_4R, so something related to visibility I'd say. But it doesn't really help me at all. 

Any suggestion?

SMALL UPDATE: It seems to be tied to the "variable water vapour option", if that's turned on the error does not appear. What could that be?