Sounds very strange for me that same error appears in your browser as well in your mail client.
Still, can you provide us some more info, in order to help you:
Which browser you use?
Which email client you use?
Did you tried to open our newsletter in any other browser?
This problem looks like a bug in your computer which can cause any program or browser plug-in installed. Nothing you should be scared of, but still, if we can help our readers, we'll give our best.