The postOfficeBox attribute is defined twice in the [ ADSchema.ps1 | https://stash.forgerock.org/projects/OPENICF/repos/powershell-connector/browse/Samples/AD/ADSchema.ps1#135,144 ]. Once as single valued attribute, second as multivalued. Documentation suggests it should be multivalued.
The fact that it is defined twice prevents from generation of the schema. Attempt to generate the generates following exception.
Removing the attr from single valued fixes the problem