Again, TomBascom + 1.
As a prerequisite, before being able to compile the application under any other version of Progress or OpenEdge, you need to be able to compile it successfully under the current version. If you are not able you are pretty much stuck. But, your vendor must be able to tell you what you need to do to be able to compile your application under the latest version they shipped. IIRC, they made a statement that you have all the source code. If they keep telling you that they can't, then I would say that they are deliberately feeding you with garbage according to their own agenda. As soon as you have all the source code, a development license of the same version and the information how your PROPATH must look like there is no reason why you should not be able to compile the whole thing successfully.
Heavy Regards, RealHeavyDude.