Problems converting pptx files with adobe connect pro

Just to be clear are you having issues with the PPTX or a PDF?

PDF files need to be fairly simple with no interactive fields and no security. If there is something in the PDF that isn't supported you'll see the Error Converting message.

PPTX files are better supported, but there are the occasional slides that get corrupted in some way, and need to be re-built so Connect can convert them to a Flash based presentation (which is what happens when you upload it). If this is the case, the easiest solution is to split the deck in half, then upload the halves. If only one fails, the bad slide(s) is in that half. Continue splitting the deck in half until you find the offending slide, then re-insert images or rebuild the slide and your presentation should upload without issue.