Here are the posts from the forum, explaining my issue and your suggestion as to what the problem is and eventually fixing it if I submit a bug report.
As usual, thanks for the help and hope to see this fixed in the future.
I'm trying to export a folder to an XML file. The folder with subfolders contains 49,509 files and 9,726 folders. It takes about 10 minutes for MediaInfo to process the selected folder. The title bar says "MediaInfo - 34,159 files", in the main window it shows the message "(You must at least open one file)", when I click on export it prompts for location to save file to, I browse to the desired location and click ok the window closes but the file is not created. If I try to choose a different view I get a pop up window that says something along lines of "Impossible ^L#D@!~", the message doesn't usually make sense.
35K files, wow... I did not test with so many files. Maybe a bug with memory. Please open a ticket:
But I will not handle such issue soon, too rare usage ;-).
As a workaround, you can try the command line version (see the Download page), in 64-bit (more memory available if you have lot of RAM), for XML:
mediainfo --Output=XML YourDirectory >Export.xml