Most likely WebEasy was deleted rather than uninstalled, or the uninstall failed.
Solution:
For WebEasy 4.0
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In the folder "C:\Program Files\InstallShield Installation Information", look for a folder called "{EA9A16A8-4B88-11D5-BF63-0050BACB9C5F}" - deleting this folder should allow you to re-install WebEasy.
If you cannot see this folder your computer may not be set to show hidden files. Please try the following:
1) Open "Windows Explorer" or "My Computer".
2) Go to the "View" or "Tools" menu and select "Folder" options.
3) On one of the pages of the options screen you should see a list of
advanced options. In this list you need to check the "show hidden files" box.
4) Click OK.
You should now be able to see the folder.
For WebEasy Professional 4.0
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In the "C:\Program Files\InstallShield Installation Information" folder, look for a folder called "{DA643ECB-948D-11D5-BF65-0050BACB9831}" - deleting this folder should allow you to re-install WebEasy Professional.