In some cases Python scripts may throw an exception containing the text:
PlxScriptingError: Missing owner object for property object!
This issue has been fixed since PLAXIS 3D 2013.01
For older versions (3D2013.0) you can resolve this by replacing server.py in your <Plaxis 3D Directory>plxscripting directory with the attached version: download the file and remove the .txt extension.