Email subscribers failing to send new post

Hi, this is the second glitch this plugin in has had in as many weeks and is causing me huge amounts of lost time and money.
I have all my setting correctly done – as this was all working perfectly and there has been no changes then I expect it to work properly anyway.
I have just written my newsletter and checked everything however it has failed to send….
Please can you recommend a suitable alternative as this current one is unreliable.

The page I need help with: [log in to see the link]