[Seaside] How to prevent session expiry

[webmail at pielka.de]

Hello,

I'm using Seaside 3.0a Pharo One-Click Image.

I tried to follow section 18.5 of seaside book to change expiry of sessions from 600 Seconds to 3000 seconds.
Due to the book there should be <WASession preferencesAt:put:> method. But I guess this is <WASession preferenceAt:put:> instead. Also if I try <self session preferenceAt: #sessionExpirySeconds put: 3000> I get the following exception: <WAAttributeNotFound signalWithKey: aSymbol>. 

I did some google research but dide not really find a solution. Does anybody have an idea?

Thanks in advance,
Kai-Uwe