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.