I encountered this error a while back, so my recollection might be a little fuzzy…
If I recall, I had the option selected to import the landuse for only the active view or maybe the limits of the model geometry. This told the program that I wanted to clip the dataset I was importing, and that’s what made it blow up; like the program was trying to do too many things at once and didn’t like it.
To resolve this, I clipped the landuse dataset externally (i.e. within GIS) and then imported to RAS Mapper, leaving that clipping option unselected.