This syntax is valid, but I don't think it does what you want to do:

$ftpobj -> put ($dir/$thefile);
[download]

(Try "$thefile = '0'" for some infinite fun.)

I think you mean:

$ftpobj->put( "$dir/$thefile" );
[download]

I'm not sure that's really the problem you're describing, however. Is this really the code you're using?