Google AdWords will remove older reports from its Report Center beginning September 2. Reports that are 6 months old or older, or before March 2, 2008, will be removed.
The data will not be removed, just the reports.
Until September 2, you can export these reports to Google Spreadsheets or .CSV files, Excel, HTML or another format.
Expect the purging of 6 month old or older reports to happen periodically going forward.
via Inside AdWords