When loading a DXF background file into a model, the program freezes or generates an error message.
First, make sure the background file is viable by opening the .DXF file in AutoCAD to see if it will open there.
If so, the issue may be with one of the supporting files. To test this, create a new folder where the model file is saved and copy just the primary model files to the new folder. For WaterCAD and WaterGEMS, these would be the .wtg and .wtg.sqlite files. For the storm and sewer products, thse would be the .stsw and .stsw.sqlite files.
Once done, open the model from the new folder location, then add the background file to the model.
Alternatively, you could delete the .dwh file from where the model is saved, then open the model and load the background file.