OK I know it sounds like it's a Vray issue but hear me out...
I have been building several houses over the past few weeks, each house is in it's own file built up from mesh and railclones objects and then grouped. I have a masterfile which just contains lighting and cameras, then I am Xref'in all the house types into the master file, I am assigning dummy objects to the xref's so I can bring in for example housetype 1, several times, each one assigned to it's own dummy.
I was almost finished bringing in all the house models when i went to give it a render, I received the error 'Unhanded Exception when instancing'. I then went into bug hunting mode, switching all xref's off, and going through each file making sure they were all perfect with no problems. I then switched them on one by one to see if it was a file specific causing the problem. again I got to about 60% through when I started getting inconsistencies with the error, sometime it would render without the error and sometimes it would flat out refuse to render. After I had tried everything else I decided to try removing ALL Railclone generators and converting them to mesh......irritatingly this fixed the problem and the entire render completed at full resolution within minutes.....
I do not understand why this is being caused, is it because of Railclone or could it be another factor? it's worth mentoning I was receiving these errors before i upgraded RC to the beta, so it's in both Beta and current versions. I am using 2018 3dMax, with Vray 3.60.0 4 - I dont think my rig is to blame as it has 128GB Ram with 44 thread 3.3GHZ 2x CPU's.