List of subscribers vanished...

Hi, I have been using this plugin for a little while with no issue. It has been emailing my subscribers every Wednesday (following my blog updates) witghough fail. Today though no email was sent out. On inspection it seems as if all the subscribers have vanished from the list. I was running a slightly out of date version of the plugin so updated it but still there are no emails listed. Have I lost all my subscribers or is there anything else I can do?