Windows Desktop Search, I believe, uses the same ifilters as SQL Server's indexing. This has apparently been an issue for years, and we are still having the issue. Apparently Aspose is putting something into the files or removing something from the files that makes the ifilter either fail to recognize the file format, or run into some internal error. One of my team members noted that the files that fail indexing on SQL Server also fail on Windows searching.
If I take a PPT created in PowerPoint, and save to the database, it can be indexed. When I save from Aspose, it cannot be indexed. If I take a file last saved by Aspose, and open it with PowerPoint, and then save it back out to the database, it can be indexed again. Are you able to interpret the difference between files to see what it is that you're putting into them or taking out of them? Even if you're putting something (like tags) into these files for your own purposes, could you perhaps provide a save option that doesn't do that?
This is a very big issue for us, and Aspose has been aware of it for years.