"Project Contains an old target model no longer supported. Project can not be opened." ?
Unfortunately, Panel Builder 6.0 doesn't support older Panels 800, e.g. PP865, PP845 etc.
It is intended only to program the new panles from ver. 6 - eg PP871, PP874...
For older panels you have to use Panel Builder 800 ver. 5.x which support them.
There are other posts in AKS about that