THis is a sure fix:

Hold down shift and right click the invalid "mp3" file, and select, open with.

Scroll down to notpad and double click it.
When notepad opens and a bunch of jargon comes up, click file and then "save as"
Rename the file as either *.exe or *.zip, whichever one you suspect it is. You MUST put quotation marks around it, so it should look something like "thisfile.exe" or "thisfile.zip" Click save, and open the file you just created. Enjoy