Hmm, still not solved this one. Have moved my site onto production server, everything working ok (so far, i have only tested with a test gateway, will be using PayPal WPS soon). still getting the error message on every other click on a filename in the downloads area of account profiles.

it downloads fine every other time, alternating with the error message "the following URL is nor a valid download link". weird.

Anyone got any ideas? Cheers!