Does the task you are actioning the "Save and close task" on have a transition from it, either to an end node or another node? I have seen this error if you forget to have a transition.
Look in the logfile, there is probably more info on the error. The error on the screen is (most of the time) useless but that is due to jsf, not jBPM
Searched for the log and check the processdefinatation.xml but error still there.
This error due to the eclipse plugin 3.0.5 crash.
Reinstalled the plugin and deploy the old par and save and close task working fine.