Fisheye and Crucible used to a be a separate software. However as of Fisheye/Crucible 2.0, they become one. Any versions of Fisheye or Crucible from version 1.6.6 that would like to upgrade to the latest version must go though this process otherwise user information will be lost due to table changes between older versions as compared to the latest. 

 During a test upgrade, no error logs on debug logging can be found that can indicate user information are lost

To upgrade to the latest version, you must upgrade to *Fisheye/Crucible 2.0 first*. Only that, you may perform an upgrade to the latest version of Fisheye/Crucible

 Please perform the upgrade on a test environment first as you would be required to upgrade twice.