I'm simply trying to upload a DPS article. The file is nothing out of the ordinary. The InDesign CC 2015 file contains a scrolling frame, an object state, and some buttons that link to PDFs. I have not re-linked the PDFs yet to new source (still linked to old HTMLResources folder). Could that be causing the problem?
I'd suspect the links to the PDFs. Try removing them and then uploading the article file.
DPS 2015 doesn't support upload of HTMLResources in the Portal. Migrated content from DPS 2014 will duplicate the contents of that folder, but many links are modified during the migration process -- so building new content and assuming old name/syntax may lead you astray. Removing the links as a test seems like a reasonable process.