I had gotten the same error. (Debian 4 etch). I ran:
zmprov -l in
wikiuser@somedomain.com password /opt/zimbra/wiki/Template Template
then restarted zimbra, and then ran:
zmprov in
wikiuser@somedomain.com password /opt/zimbra/wiki/Template Template
make sure your zimbra user is setup.
zmprov gacf | grep -i notebook
zimbraNotebookAccount:
wikiuser@somedomain.com
zimbraNotebookFolderCacheSize: 1024
zimbraNotebookMaxCachedTemplatesPerFolder: 256
zimbraNotebookPageCacheSize: 10240