TC, in that case I’m absolutely sure what has happened is that you have burnt these files (inadvertently) as audio files, and even though they might have been mp3s originally, your copying software has converted them to audio, to be placed on an audio CD.
Re-ripping them is the easiest (if not the only) solution that I can think of.
P.S. Even if the files are renamed, it should not change the filesize. 1kb is the size you would expect from a cda file, not an mp3.
I think the fact that everyone reckons it’s the same thing should tell you something.
FYI, some info from the interweb…
“Another place of confusion arises when people put a commercial audio CD in their CD-ROM drive. If you right click on “My Computer” on your Desktop, select “Open” and then right click on your CD-ROM drive and select “Open” you will see a window full of 1 KB files. The names will be Track01.cda, Track02.cda, etc. The CDA extension is not a true file format. It is just a way of referring to audio tracks. Only software that understands the true nature of the CDA extension, such as CD Recording software, will know how to properly handle it. To illustrate my point try copying or dragging and dropping a CDA type file onto your Desktop. Now right-click it and select “Properties”. Notice the file is only 44 bytes in size. Thus it is not the audio content data but it is also not a Windows shortcut. Close the “Properties” window. Now right-click the CDA file again and select either “Open” or “Play”. In each case you will get a dialog box that says “Can’t play CD track. CD tracks must be played from local CD drive.” Now if you go back to your original CD-ROM drive window, right-click any of those CDA files and select “Open” or “Play” the music will start playing.”