Sorry for replying to myself again, but I can't get this off my mind. I reinstalled funambol again today, this time version 8.7.0 together with funambol-sogo-1.0.8, as described in the manual. SOGo itself is at version 1.3.6.
The error still is exactly the same, no matter which client (Android or Symbian) or whether the user does have calendar entries in the db. Any help would be really appreciated. -- users@sogo.nu https://inverse.ca/sogo/lists