I'm surprised this works at all - it certainly isn't doing what you think it is. The :

while(<@source>)
{
  ...
}
[download]

is actually doing a glob based on the contents of the file and is making $_ the actual line where (not unexpectedly) there isn't a match.

I think you meant:

foreach ( @source )
{
   ...
}
[download]

or

while(<SOURCE>)
{
   ...
}
[download]

if the latter you will need to move the close to after the loop.

/J\