Using newest beta in Win7-32. I was trying to confirm the /help file saying "If too many files are selected, $msfile() returns -1."

To recreate:

1. Created a subfolder beneath $sysdir(downloads) and copied 200 files into it.
2. Type: //echo -a $msfile(c:\that-path\)
3. Click into the dialog to set focus, then use Control-A to select all files
4. Click 'open' and it echoes the count of selected files.
5. I then copied a few files into the folder and repeated #2-4 each time I added a few more files.
6. Once the filecount reached around 216 it crashed mIRC.

Code:
//mkdir crash | bset &a -1 0 | var %a 1500 | while (%a) { bwrite -c crash\file.txt $+ %a -1 -1 &a | dec %a } | echo -a $msfile(crash\)


Wims tested it and he didn't crash with 216 files, but he did crash with 1500. So I retested with the above command, and it didn't crash until i increased the filecount to around 360. So the difference might be different memory levels or shorter filenames.