Hi, Pawel -
I've not verified this, but I believe the restriction is that you cannot utilize these functions when running the application from the IDE when the app has been converted to Solution format. Once compiled/deployed, I think these functions will work normally. My guess is that in order for these functions to work, they require access to the intermediate object code that is kept in a PBL (or compiled into PBD/DLL's). Only source code is available in a Solution-based app.
The same restriction is in place for the LibraryDirectory and LibraryDirectoryEx PowerScript functions.
If this is a critical issue for you, you will need to keep your application in a Workspace and continue to use PBL's.
Best regards, John