[horde] back trace config error

[toto]

Hello, world!
I'm trying to install horde 3.0.2 without success on a gentoo box. 
When I try to configure horde with the web interface I allways got the
message "There was an error in the configuration form. Perhaps you
left out a required field." and under that, "This form has already
been processed." when I click on "Generate Horde Configuration". 
I've trying with a lot of different parameters (with or without
logging, with different DataTree systems, token authentification etc
etc) but without results.
Db is working fine.

What could I try to trace the error?
I've tried with Horde 3.0.1 and 3.0.3 in tar.gz form and the 3.0.2 in
gentoo package and tar.gz, all without results. Horde2.2.7 works fine.

Thanks for your help.
tots