Ansys Employee
What version of Ansys Mechanical and the ACT are you using? You need to make sure the ACT version is compatible with the Mechanical version. You can check you solve.out file, see what element types have been generated to make sure piezoelectric definitions are correctly done through the ACT (solid226/227 element types).
For the postprocessing error, you can try insert a user defined result and set it to VOLT. See if this helps. Or insert a command object to print/plot the volt dof.