If LC can't fully open the DWG, then it will throw the message you saw.
Your best bet is to ask for a dxf to the person who provided you the
dwg, or relay on some dwg to dxf converter out there.
That said, IF you are able to compile LC and IF you assume to lose some
of the data in the DWG and IF you are lucky, you could modify the code
that checks for errors in a DWG and let LC try to open it anyway.
From my experience this helps in about 20% of DWGs that pose problems,
at the cost of losing some unrecognized entities and lose some format,
the other DWGs are plainly unopenable with LC