Our PhotoPost Pro and vbGallery products use the SWFUpload flash uploader and there are several things to consider when enabling this feature.
The feature while allowing you to upload multiple files to the server still is limited by your server's PHP limits. Therefore all the things held true work the same for flash uploading.
1. If you want to upload a file larger than 2mb then in your php.ini file on the server you will need to change the following variable to what you need to support the filesizes you want to upload. By default on alot of PHP setups this is 2mb.
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2. Imagemagick or GD2? Well my opinion is to use Imagemagick if you can since it is not prone to stealing memory from PHP like GD2 which is part of PHP.
3. Flash Uploader will not work with Mod Security installed on the server. Mod Security prevents things from working. Now there is a tweak you can do in your .htaccess file in your gallery directory at top you can try placing this and seeing if this helps you allow the flash uploader to work with mod security on.
Code:
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If that does not work then the only way to get flash uploading to work would be to turn it off.