Code 239 during installation of MultiZilla v1.8.3.4e

Hi there,

I'm trying to install Multizilla to regain some tab functionalities I 
miss, but I keep getting an error code 239. I have tried reinstalling, 
both through downloading and direct installation, and to find 
information about this problem on the website, but to no avail.

How do I correct the situation? I am using Mozilla/5.0 (Windows; U; 
Windows NT 5.0; fr-FR; rv:1.8.1.12) Gecko/20080201 SeaMonkey/1.1.8 and 
have administrator privileges.

Thanks for your help!

S.