I checked my registry, and there wasn't an entry for
HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\CheckPoint\Endpoint Security.
So I made one anyway, and then added in the entries for the values "UninstPwdHashDA" and "UninstPwdSaltDA" (d-word) and set the value to either 1 or 0 (can't remember which one, as the un-install worked and then deleted the registry key!
The above solution worked for me. I created the entry "UninstPwdHashDA" and "UninstPwdSaltDA" [D-word] and set value as 0 (default) using RegEdit. The uninstaller accepted the default password and Endpoint security client got uninstalled. In my case the uninstaller removed the registry entry.