It would be helpful if you occoured the crash dump that was generated at the location that is displayed in the error message.
Also, is it reproducable, i.e. can you force the crash by loading the same file twice? If no, does it use any plugins?

I tried to upload the crash dump when I submitted the report but the page kept telling me that it's an invalid file type for upload. I just uploaded it to Dropbox, though: https://db.tt/ErDHlIkm

It seems to happen before I can even select a file to open from the file browser. I click Open File, the file browser opens up, the same error message displays, and once I click OK to close the message the program crashes. I tried this at least 5 times and it behaved exactly the same each time.

It doesn't use any plugins as far as I know.

Memory dumps can be quite big, hence you'd have to zip it before uploading to the issue tracker (we're not a file hoster after all).

Anyway, this crash appears to happen deep in the system, i.e. not somewhere in our own code. Are you sure that no other applications are affected by this? All OpenMPT odes is opening the system's file browser, and then the file browser code crashes.

In case you can still reproduce the problem and can confirm that it only happens in OpenMPT, please get the latest test version at http://sagagames.de/stuff/mptrack.exe - if this one also crashes, please start it with the command line option /fullMemDump to generate a complete memory dump (this one will be severeal hundred MB in size instead of just a few hundred KB). Please compress it and upload it somewhere.

I've tried almost all of the programs on my computer and OpenMPT is still the only one that seems to be affected. The test version behaves the same as before except that it doesn't show the error message before crashing.

Is the complete memory dump in the same location as the regular crash dumps? I can't seem to find it.

Yeah, it should be created at %TEMP%\OpenMPT Crash Files. Does the crash dump get created when you don't specify the /fullMemDump switch? Do I understand correctly that you don't have any files open in OpenMPT while the crash happens?

Edit: Also, another thing I'd like you to try to copy mptrack.exe to a different folder and start it with the /portable command line switch from there.

The dump does get created when I don't use the switch. I don't usually have any files open when I crash the program, but it's possible to have one open while it happens if I opened a file from the recently opened file list at the bottom of the File menu.

I just tried using the /portable command and that seems to make the program work correctly without crashing.

Please test if running from the new folder without the /portable switch results in no crash as well.
Also, please share your mptrack.ini from the non-portable version (located in %APPDATA%\OpenMPT).

It crashed when I ran it without the switch. Here's the .ini: https://db.tt/xIIKJXWT

That's really strange. The only difference between using the switch and leaving it out would be that OpenMPT doesn't try to open the file selector in the default location (which would be Songs_Directory=C:\Users\Vincent\Music\MPTracker MODs in your case). Just to see if this is really the cause for the problem, locate the line starting with Songs_Directory in the portable mptrack.ini (which you can find in the same directory as the mptrack.exe that you used the /portable switch with) and replace it with the Songs_Directory line quoted above.

I tried that and it still crashed, but I discovered that if I changed the default song directory through the settings from "MPTracker MODs" to "My MPT Modules" (where I save the ones that I write) it suddenly works. Could it be something with that specific folder?

This confirms my suspicion but I still don't know why it causes the problem... And I somehow think that I will never get to know because it seems like a system issue to me. But let's try a few things:

• Does navigating to that folder from somewhere else make OpenMPT crash as well?
• Try to rename that folder to something different. Does it still crash?
• If it does, try copying the folder. Does the new copy still make OpenMPT crash?

I think it is entirely an issue with my system now, because accessing the folder or any of its copies causes Windows Explorer itself to crash.

That's kind of what I suspected. It might be some damage in your file system. Anyway, I guess this a good point in time to close this issue. Good luck with rescuing that folder. ;)