 a Clinically stable and are in the residual non-acute phase of their illness for at least 8 weeks b Current antipsychotic and concomitant psychotropic medications must meet the criteria below: b-1 Maintained on current atypical second generation antipsychotic medications in any approved dosage form other than Clozapine and on current dose for at least 8 weeks prior to randomisation, andor b-2 Maintained on current typical first generation antipsychotic medications and on current dose for at least 6 months, optionally combined with anticholinergics if treated with a stable dose for at least 6 months prior to randomisation, andor b-3 Maintained on current concomitant psychotropic medications other than anticholinergics, antiepileptics and lithium, and on current dose for at least 8 weeks prior to randomisation. Antiepileptics and lithium are allowed if initiated at least 6 months prior to randomisation. 