Red X on slide thumbnails in Master View

I know this is an old thread, but I have a user who is experiencing this issue.  64bit OS with 32bit Office 2013 installed.  Once the red X appears, cannot save presentation.  Closing PP and reopening allows them to continue to work, but if changes were made since last save and red X appears, all changes are lost.  All office and OS updates have been applied, so that's not an issue.  even happens on small (7mb) presentations.  Any help from MS would be appreciated.

I got the Red X to go away by hiding and unhiding the slides with the Xs showing.

Good luck

It's March 2016 and I do not find a MS fix for this bug. Please correct me if I'm wrong.

I've been using PPT 2013 daily for several months in a large corporate environment without incident until last week.  Manager was working on an 80+ slide deck. Everything was good until he attempted to copy a  SmartArt graphic from another deck and paste it into his deck. With that action (which we have duplicated and confirmed), his file suddenly went "Read Only" and red Xs (large and small) showed up in thumbnails, bullets (which are images) and embedded images and backgrounds.  I have screen shots below if anyone is interested. I blurred out confidential information.  The SmartArt that caused all the problems is the hourglass pyramids (slide 4).

Today, a deck someone in the office sent me was looking great, including the thumbnail views on the left. Then, while showing the deck's owner how to use Adjust > Color and Adjust > Corrections options, odd things began to happen. Background image disappeared entirely while trying to adjust the color saturation using one of the presets. And then a large red X appeared in one slide in the thumbnails view. 

While I have not figured out a fix, I have made an observation that may, or may not help the MS team.  The SmartArt that was copied and pasted into my manager's deck originated in a deck that was originally built on a Mac.

I believe the deck that gave me a red X today was at one point opened on a Mac before I got it. 

Jodi-

I found an immediate cure was to simply drag the width of the thumbnail column slightly wider. This caused all thumbnails which were red crosses to resolve to proper thumbnails. You can then drag the column width back again if necessary.

I just encountered this problem. After editing and resizing some pictures, I found that the thumbnails displayed a red x. All I did was resize the image and made it a bit smaller, and the thumbnail went back to normal. It might be PPT's way of telling you that you've done something it doesn't like.