I've been using UPK 3.5.1 Developer for years with Office 2003 (yes, I know we should upgrade, but that's out of my control), and have successfully published many times. After my latest publishing, the following error showed in the Activity Log:
Task: Job Aid / Postprocessing document
Comment: Invalid docx file format odpub://int/PlayerPackage/Temp/03d444ee-681b-406b-aba2-cd4b669702e2_JOBAID.docx
All of the other job aids have published to a .doc format, so I'm not sure why this one is behaving differently. I located the offending topic, and in UPK, the preview provides a similar error when I try to preview the job aid. Strangely enough though, in the published project, the job aid for that topic prints just fine. I know I can just ignore the error since the finished product works, but I'm just wondering if anyone has some insight as to why this error occurred.