What this solution fixes:
1) Progress bar on uploading is not showing
2) You are getting an error when uploading "Failed to find flength file"
Please, make sure that your custom php.ini contains the following:
upload_max_filesize = 100M post_max_size = 100M output_buffering = On max_execution_time = 1000 max_input_time = 1000 session.gc_maxlifetime = 14400 enable_dl = on
And .htaccess:
SecFilterEngine Off SecFilterScanPOST Off