mp3 protected content not recognised by iTunes

I use securesite to protect access to mp3 files. Our customers mostly use iTunes to download them. With securesite-6.x-2.2 this worked like a dream. However after upgrading to securesite-6.x-2.3, iTunes started to complain that the file was either corrupt or of a type that it couldn't play. Checking our server logs, iTunes was aborting the download after only 187 bytes. (always 187 bytes).

Downgrading back to securesite-6.x-2.2 resolved the problem.