In some random cases, when the model uses the interpolate pore pressures option, the program may give a bug report while preparing the calculation. The bug report in this case shows the following exception message: Boundary intersection sort fails: Master CutObject is not in the sorted list.
In this case the program has a problem determining the (interpolated) water pressures on one or more of the intersected objects in the model.
This issue is resolved since PLAXIS 3D AE.02
For older versions, a work around is to use the User-defined option to manually specify the desired pore pressures in the volumes that would otherwise have used the interpolate option.