The first line is in reference to the working area of a SolidWorks work environment, you have a 1km^3 volume to work in, so anything that is further than 500m away from the origin will not import.
If you have imported larger file size in the past I suspect that when it was originally modeled in AutoCAD it was done so more than 500m from the origin.
I would suggest ending the import and try locating the part in AutoCAD more central to the origin.
I had a bug in 2016 SP1.0 where importing step assemblies i would wrongly get the error that it is larger than 1km part, upgrading to 2016 SP2.0 EV fixed that for me this could also be an issue if you know your part is within 500m of the origin
Yeah not sure how much stuff is away from the origin as the original autocad version once converted had half the items in 1 location and the other a mile away and the origin was not near either of them, like postage stamp viewwhen you viewed all.
It ran for about 20 hours and then stalled out at 20011520k worth of memory, and I had some other tasks to get done, may leave it this weekend and see what happens if anything
Thanks for the responses,