Invalid argument supplied for foreach() in ../dragndrop_uploads/module/filefield.inc line 13

I'm not sure what's causing this error, but it can be overcome by changing line 13 from

foreach ($content['fields'] as $field) {

to

foreach ((array)$content['fields'] as $field) {

Maybe someday PHP's array functions will be smart enough to handle scalars, but in the meantime (array) is a handy workaround.