Sometimes FreeAgent Pro drives will display a FreeAgent Tools diagnostic failure when connected via the eSATA interface.
By design, FreeAgent drives are not designed to be tested with the FreeAgent Tools utility when connected via eSATA. If you do try to run a diagnostic test, it is supposed to give a message stating that the tools are only available when connected via USB.
Due to the many different controllers out there, sometimes the tests are available. In these cases, if you test the drive while connected via eSATA, you will get a failure every time.
This does not mean that the drive is failing. Rather, this occurs because the test is not supported when the drive connected via eSATA.
If you are concerned about the health of the drive, please connect the drive through USB and then run the diagnostic test. If this test passes then you should consider your drive healthy.