I continue to get this issue and the memory allocation is NOT the problem.
I have found that the students who are getting this error are those who are using Chromebooks.
I have been forced to allow those students alternate methods to upload image and pdf results to Discussions (rather than use the tool bar to insert an image or document into the Rich Text Editor so that other students reading the post don't have to download a file and open it up to view it, which they won't do).