I happen to see this uu_upload.pl download prompt error when installing phpmotion on a subfolder. This is because Apache doesn’t understand this perl file in cgi-bin.

Here is a fix which worked for me

Create a .htaccess file in cgi-bin of the subfolder and add the entry

  Options +ExecCGI
 AddHandler cgi-script .pl  

This error can also happen if you haven’t given the correct path for cgi-bin in uploader_conlib.php file

 
     $path_to_upload_script      = '/myvideos/cgi-bin/uu_upload.pl'; 
     $path_to_ini_status_script  = '/myvideos/cgi-bin/uu_ini_status.pl'; 

myvideos replace it with subfolder name.