Many time errors of this type can be resolved by very simple means. A few things to try are below (though sometimes I take some heat for suggesting them.) ;)
* Reboot, and start with a fresh browser - logging in from adwords.google.com rather than a bookmark or similar
* Try a different browser
* Update browser to most current version
* clear cache and cookies
Hope these thing will help, if you are still having this issue.
AWA