Hi Fran,
Can you provide a screen shot of the error? I'm not sure if I've seen that particular one before. A couple of things to try. First, log in and out of Method. What I mean by this is to actually go to the top right of the screen and select "Sign out". This will clear the cookie and set a new one the next time you log in.
If that doesn't work, I'd try clearing the cache on your browser completely and trying again. It's more than likely a local computer issue.
- Adam