[imp] Strange Problem

[cyx]

Hi, some of my users (including me) have the following problem: if they
click in the mail compose window on  the To: or Cc: link, a new window opens
with some error message in red in it and in the window appears a new
instance of horde itself. Normally (some users get that too) the window
should display the adressbook. I think this has to be some misconfigurations
oft he users itself, but I can't figure out which one.  Tried every Turba,
Imp (even horde)  configuratzon page/setting, nothing helped.

Any idea, where to search ?

Regards 

Werner