When trying to log in to Dropbox-plugin i Moodle:
ERROR: Invalid JSON string
array(1) {
["{"error": "You're using an older version of the Dropbox API with a new API key. Please use the latest version."}"]=>
string(0) ""
}
Seems like the Dropbox-plugin must be updated to support Dropbox API v1:
http://forums.dropbox.com/topic.php?id=46501&replies=32
http://forums.dropbox.com/topic.php?id=48097&replies=6
Yes, Moodle Dropbox plugin must be updated to work with Dropbox API v1. It already exists a issue in the Tracker asking for that:
http://tracker.moodle.org/browse/MDL-29960
If you're interested in getting it done as I do you should vote for it (I've already did), 
Please look at
http://forums.dropbox.com/topic.php?id=48097&replies=17#post-366818
But I think this is something for the Moodle developers!