When you deploy a PowerBuilder Web Forms application to IIS
7 or later, the application is deployed to a PowerBuilder-specific
application pool named PBAppPool.

PBAppPool uses the default application
pool identity, which is NetworkService on IIS 7, and ApplicationPoolIdentity
on IIS 7.5. However several Web Forms application features, including
the creation of permanent user accounts, SSL authentication, and
DataWindow Print and SaveAs commands,
do not work with the default IIS 7.5 application pool identity.
To enable these features, you must change the PBAppPool application
pool identiity to NetworkService.

See Changing Application Pool Identity for IIS 7.5.