I am seeing several reports from two forum threads, including Google AdWords Help and WebmasterWorld that some users are having time out or session issues with using the Google Keyword Tool within the AdWords interface.
One person said that the new beta keyword tool is fine, while the other one said only the new keyword tool is having issues. It seems to me to be a cookie or caching issue with these folks browsers. Maybe Google did make a slight change that is impacting older browsers or maybe something went wrong on these user's browsers. I am not sure, but I know it is working for me.
Google AdWords representative, Bindu said:
I'd strongly recommend you upgrade to the latest version of your browser and/or clear cache and cookies.
The error some of these users are getting is:
Your session has expired. Please return to the AdWords homepage and login again.
Here are instructions on clearing cookies and instructions.
Forum discussion at Google AdWords Help.