If that's not that case and you're moving quickly through AdWords, then you may need to delete your cookies and empty your browser's cache.
* Consider trying another browser
* Update your browser to a recent version, if it is very old
* Check your browser security settings:
Microsoft Internet Explorer (MS IE)
1. Select 'Tools' from the MS IE browser menu.
2. Select 'Internet Options.'
3. Select the 'Advanced' tab.
4. Under 'Security,' check both 'Use SSL 2.0' and 'Use SSL 3.0.'
Other settings to check (sample steps for IE shown):
1. Click 'Tools' at the top of your IE browser window.
2. Select 'Internet Options' from the menu.
3. Under the Security Tab go the 'Trusted Sites' icon.
4. Click 'Sites', enter 'https://adwords.google.com', and 'Add'.
5. Click 'Ok'
And:
1. Click 'Tools' at the top of your IE browser window.
2. Select 'Internet Options' from the menu.
3. Under the Privacy Tab go the 'Trusted Sites' icon.
4. Click 'Edit', enter 'google.com', and 'Allow'.
5. Click 'Ok'.
I hope that these steps will help. If not, I'd suggest writing to AdWords Support, describing your problem and when it happens, your operating system, browser (and version), etc.
AWA