Additional to all the good advice you already got, please try to debug if %FORM is really populated ( I doubt)

Something like

 use Data::Dumper; 
 print MAIL "=== Check Form: \n",
      Dumper \%FORM, 
      "\n=== end check\n" ;
[download]

should do.

Most likely you have a typo somewhere and forgot to switch on strict and warnings to catch them.