Hi, 

I have WLMM 15.4.3538.513

Windows 10

I loaded and successfully edited a number of AVI video clips over a number of projects.  I then closed them to come back to them later, re-opened the first and was able to successfully finalse and save it.  When I opened the second (and subsequent) projects, many videos were black, or had the yellow error showing claiming 'missing files'.  Now when I open the first project again, it also has issues... how can it be okay one moment, and then completely stuffed the next???

The files have not moved, there are no missing codecs and everything plays fine in Windows Media Player.