[imp] setup does not respond after copying the imp directory

[Joachim Nolten]

After performing a new install of Horde 3.0, everything is functioning 
perfectly.
I have configured backend, auth, etc.

But as soon as I untar and copy Imp 4.0 to the Horde base dir, the 
setup page for administrator
stops responding. I am still able to configure the mail through 
/admin/setup/config.php?app=imp.
Also no functionality seems to be lost. So presumably, the fault is 
with /admin/setup/index.php not
parsing the applications list or not accepting imp as a functioning 
application.

I had no problems with this before, using rc3, but possibly a server 
setup change is to blame.
I'm at a loss. I've tried every setup imaginable, different auth 
mechanisms, with or without
db backend. I have checked file permissions. Has there been an implicit 
requirement change between
rc3 and final? Any help is welcome.

Regards.