The getboundingbox method gives this error every now and then.
So far it seems to be caused by an empty blockref, perhaps there are other causes I don't know.
On googling I found one post mentioning that it seems to happen on the ashade layer.
On I checking out solprof I found that it still makes the hidden line block on item with no hidden edges ,
a block with a zero count (A bit bugsy there cad).
On making a new getboundary function that deleted the offending empty blockrefs and its parent block,
I found the whole idea a bit useless as getboundingbox is used in so many for each loops and on deleting the blockref
it'll error out with an automation error, or catastrophic or something.
The only thing I can think of is running an empty block purge before making the loop.
Any ideas?