To me it looks like it failed to uninstall your old version of 7.5. We had issues with that as well. First thing I would do is call support.
If your going to try yourself....
We saw this a lot on the clients we had.
Try going to control panel - programs and try to uninstall Service Desk.
Re-install 7.5 if remove fails (it probably will fail to remove but worth a try).
Once re-installed you should now be able to remove 7.5 from Control Panel - Programs.
7.5 is the last version to have install/remove issues so from now on you SHOULD have no issues.