I'm sorry you're having trouble. Could you please let me know exactly which button or link you're clicking, on which page, when you get this blank page and error message? Could you provide a link to the page here?
It might also be useful if you could upload a screenshot of the page, including the browser's address bar, to help in troubleshooting. Here's a guide on how to make a screenshot, if you're not sure: http://en.support.wordpress.com/make-a-screenshot/
You can then upload the screenshot in your Media Library and then post a link or let me know the name of the file so I can take a look.
Thanks for your help!