Importing a model set from a previous version results in large number of errors like example [1] due to broken references. In one example set there were 900+ of these errors related to 3 model files. To correct, the model files need to have Edit -> Modeling -> Validate Transformations action run on each model individually.

[1] Sql transformation in the model mymodel1 contains the unresolved reference file:/C:/jbdevstudio/8.1.0.GA/workspaces/mymodel2.xmi