I suspect that he has a "bootleg archive" of the project, where it's not in the proper directory and wasn't compressed as a *.APA file by the FactoryTalk Application Manager.
Open FactoryTalk View Studio, select "Machine Edition" if necessary, and see if the Oven project is in the list of existing applications.
If it is, just open it up and you should have editing access to the project.
If not, you're going to have to carefully import it into the FactoryTalk environment.
On my XP computer with FactoryTalk View Studio ME 6.10, the project directory is
C:\Documents and Settings\All Users\Documents\RSView Enterprise\ME\HMI Projects
If your project file is not in that diretory, DO NOT just copy the project file and subdirectories into that folder. Everything's carefully registered and logged and directed through FactoryTalk, rather than simply browsed and found in the directory.
Importation is straightforward; you create a New project, select Import, then browse to the *.MED file (which, again, must not be in the HMI Project directory yet).