When you say that you modelled, it is important how you modelled the buried piping. Especially, bends, elbows and close lengths to these fittings need to have sufficient number of nodes in the model. Span lengths between nodes on the buried pipe are have to be in line with CAESAR II user guide or shorter. If you have already done this, check units of your inputs, especially the densities.

After checking you still cannot solve the problems you are facing you need to send your model to the Coade to ask for their help.