Just for the record:
The only way I was able to reproduce this behavior is if you some how call more than one time ad_returnfile_background within a script. First time the file will be delivered as expected, because "ns_conn channel" will return a valid tcl channel. Second time the error you mentioned is raised.
The error could differ depending on which version of xotcl-core one is running. On recent versions, something like this will be raised:
Unknown error: 0
while executing
"ns_conn channel"
(procedure "returnfile" line 6)
I did check the index.vuh file under file-storage/www/download and i dont see how ad_returnfile_background would be called more than once. Probably at the time you wrote this post it was possible to fall into such situation; should not be the case with a recent version of file-storage.
