It look like both the Image Processor script and the Image Processor Pro script will not process open document that have no associated backing file. When you open a PDF file and use options for Photoshop to use opening the PDF the documents that open are new document the source PDF files have been processes into a new documents that have not been saved so the open document has no associated backing file.
I mad a simple test. Opened a PDF. Tried the two scripts they failed. Then I saved the open document and the ran the Image processor on the still open document that had been saved as a tif. The image processor worked and saved a jpg.