Google has confirmed a bug impacting some AdWords advertisers trying to use the AdWords Editor. Some advertisers won't be able to see some of their accounts within the editor.
The confirmation came from a Google AdWords representative named Bindu. You can see the post in the Google AdWords Help forum. Bindu said:
There is an issue with some accounts trying to access the AdWords Editor where they see permission errors. Please know that this s a known issue that is being worked on, and there is not current workaround. You will still be able to make changes to your account from the front end.
So if you think your data is gone, it is not, there is just a bug preventing you from seeing it within the AdWords Editor.
Google did not give an estimated time for when this will be fixed and I do not know how many advertisers are impacted by this bug.
Forum discussion at Google AdWords Help.

Comments:
Mario Francesevic
12/17/2010 12:57 pm
I've noticed it before almost two months and reported it. Hope they will fix it soon :(
Roe
12/17/2010 11:07 pm
I've Found another goof in Google Adwords, showing different Ads from our campaign on Google search results. results for keywords that not assign to that specif ad.