I am experiencing a similar problem, where i cannot upload anything larger then 1.5GB. I monitor the uploading process, and i confirm that file uploads up to %100, then i get the following error "The uploaded file exceeds the MAX_FILE_SIZE directive that was specified in the HTML form".
On my .htaccess, i set the following limits:
php_value upload_max_filesize 2048M
php_value post_max_size 3096M
php_value max_file_uploads 120
php_value max_input_time -1
php_value max_execution_time 0
php_value memory_limit 128M
I increased memory limit up to 3-4GB [i only have 4GB memory], set max_execution_time as much as an hr [3600 seconds], set post_max_size to 9GB, set upload max_filesize to 4-5GB.. Whatever i do, i cannot upload a file that is larger then 1.5GB. I also set " MaxRequestLen 5180736000 " in my http.conf file. i am running out of ideas.. For the basic testing, i tried a 1.9GB file, and no dice..