it now says that no such file or directory exists

Okay, there's more going on than just a permissions issue, then. The file your code is trying to open doesn't exist, which may mean that it's got the wrong path or filename. I tested the following code:

use constant USER_DATA => '../data/users/';
my $username = "root";
my $userfile = USER_DATA.$username;
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This sets $userfile to "../data/users/root", which is probably what you intended. (The $username variable did get set to "root", yes? That should be printed in parentheses in the error page, using the code I posted.)

However, it's a relative path, which leads me to wonder whether the current directory is different from what you thought it was. I believe that when Apache calls a CGI script it sets the current directory to the directory containing the script. So, if your script is /var/www/cgi-bin/something.cgi, the file you're trying to open is /var/www/data/users/root (This is a *nix system, not Win32, right?)

You're sure that file exists?

$;=sub{$/};@;=map{my($a,$b)=($_,$;);$;=sub{$a.$b->()}}
split//,".rekcah lreP rehtona tsuJ";$\=$ ;->();print$/
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Are you sure thats the same path your other form is using to save the files to? Try outputting $userfile as well, to see what that contains? You can check if a file exists using '-e', so you could try if(-e $userfile) { display_page("Can't find $userfile") } or something similar..

C.