I host my own website where I sell mp3s of my music and it's been running fine for several years. But recently I noticed a strange problem where some of the mp3 preview files no longer play depending on their filename.

The files are played through a Wordpress Flash player plugin and never used to present any problems but some of them now just don't play.

For example, there's a track called "track1_preview.mp3" that now does nothing when played - the file doesn't appear to even be buffering. But I noticed if I change the filename to certain characters it then plays fine. E.g. if I change it to "track1_review.mp3" (dropping the "p") or "track1_1preview.mp3" (adding a "1") it plays fine but if I change it to "track1preview.mp3" or even "a1.mp3" it won't play again. I've tried all sorts of combinations thinking it might be due to length of name or use of underscores etc but there's no pattern. Sometimes just adding a random letter in the filename will take it from unplayable to playable.

This is happening in the latest version of Firefox with the latest Flash version but to make it more complicated, I have 2 user profiles in Firefox, both with exactly the same plugins. On one profile some tracks don't play, on the other they do. I've tried clearing the cache but makes no difference.

I can't understand, firstly how a filename like "track1_preview.mp3" now won't play but also how changing it to "track1_1preview.mp3" suddenly makes it playable. And given the fact that there used to be no problem until fairly recently.

Can anyone suggest why adding or removing certain characters would cause a file to become unplayable?

As I say, it's been running fine for several years and only recently happened and also only seems to be FF specific.

If I enter the mp3 URL link directly in the browser it plays fine in the native player (Quicktime) but won't play via Flash without altering the filename and it's not down to the particular Flash player as I've tried several and they all exhibit it.