On occasion, something (the cause is irrelevant) may cause a wysiwyg or Vivien installation or uninstallation to fail. The solution to all such issues is simple: click the following link in order to download a .zip file containing the CAST Software Cleanup Tool, and run this tool in order to remove the failed (un)installation; once complete, you will be able to install the same version of wysiwyg or Vivien once again.
Should you require them, the instructions for how to use this tool are also included in the downloaded .zip file.