Support for Portfolio Server and Netpublish 8.5 ended about 3 years ago. I would encourage you to upgrade your system in the near future.
If there have been no changes with the site files, then the issue probably stems from the catalog itself. My recommendation would be to unserve the catalog, then recover it to remove any cruft that may be hiding in the database.
Here’s an old writeup that explains the steps:
Here are the instructions for recovering a catalog.
If the catalog is not being used with Portfolio Server, proceed to step 1) below. If it is a served catalog, it will need to be unserved and then copied to a computer that has Portfolio installed on it.
To unserve a catalog, open Portfolio, then go to the File menu and select “Administer Server”. Enter your Portfolio Server admin password and click “OK”. You’ll then see the admin window. Select the catalog to be unserved and click on the “Unserve…” button. Hit the “Done” button when you’re finished with that. Typically the catalog will be stored in the Extensis Portfolio Server folder, inside a folder named “Catalogs”. Copy it from there to the computer that will be recovering the catalog, then follow these steps:
In case you have any catalog open, go ahead and close them, then go to the Catalog menu and select the ‘Recover’ command.
You’ll be prompted to open a catalog to recover.
Then you’ll be asked to save the recovered version under a new name or location.
Portfolio will then go through and clean up the database structure.
When that’s done, you can delete the previous copy of the catalog and continue working in the new recovered copy.
If the catalog was previously served, copy the recovered copy of the catalog back to the Portfolio Server “Catalogs” folder. You can rename it back to the original catalog’s name before serving it. If it’s a catalog that’s being used by Netpublish server, it has to be named exactly the same as before. After that, use the Portfolio Server Administration dialogue to serve the catalog again. You may delete the original catalog once you’re done with the above procedures.