This error means that the Connexion client was not able to uninstall the 2.63 version correctly. To correct this, do the following:
Important! If you've created custom 2.63 macro scripts and want to keep them, make sure you copy out your C:\Program Files (x86)\OCLC\Connexion\Program\Macros folder to a network drive before deleting the Program Files (x86) Connexion folder.
You should be able to bring up Connexion without error. If not, please contact OCLC Support with your library symbol, the steps you have taken and the error you are getting.
Additional information