When trying to deploy a project within PowerBuilder 10.5 I receive the message:
Unable to open this project because the add-on software that was used to create it could not be found. Perhaps this project was built on another system?
The resolution to this was listed in an old newsgroup posting: Unable to open Project because an add-on software not found
The issue was that I had two sets of PowerBuilder dll's in the path, but the location where the dll's for the IDE were located was listed as the second one in the path. I modified the system path so the set of dll's that the IDE uses came first in the path and then the issue went away.