The current version of SetiStat doesn't work with the old client anymore.
If you are still using the classic SETI@home client, have a look at
http://www.rexi.org/downloads/setistat/setistat-0.8.1.tar.bz2
It is the last release for the classic client. The current release and all
upcoming releases will work only with the new BOINC client.
 
The current release is not as well tested as the old releases as most of it is
written from scratch. So, if you find any bugs, please drop me a line so I can
fix them. You can consider the 0.8.9x releases as beta releases for the upcoming
0.9 release, which will finally complete BOINC support and will be stable again.
Hopefully.

Precompiled clients for BOINC are available for Linux, Mac OS X and Solaris.
SetiStat runs on all of this platforms.
