Import issue wt.util.WTException: RepresentableObjectRef ?

When I import from a 10.1 into another 10.1 system ( we tried and the same issue for 11.0 to 11.0) I get the below error. I would just like to know what does this error refer to and does anyone have a solution to this?

Nested exception is: wt.util.WTException: RepresentableObjectRef absent for Representation