It's a while since I used abcexplorer but I think there should be a window which shows each file as a text file. There should be an option to open it if it is closed. It might be called an 'edit' window. If you can copy one of those text files from the edit window and paste it into mudcat I could try it out on my machine. Just the file from one tune. It should start with

X:1

and end at the first space. abc files are quite small, even collections of tunes are small by today's standards.

Post a file here and maybe we can sort it out.