Horde IMP's address book: error creating object

[Indefual]

1) When I or anyone with an email account tries to add a contact to the address book the server says

An error occured while trying to add this object. Contact your administrator.

What do I have to do to fix this? I checked out the manuals/FAQs for both Admin and Users at horde.org but they don't list this error.

2) This is the 'Email Management' section, but the description only talks about POP3 mail et cetera. Is there a specific place for webmail / Horde IMP?

Thank you in advace for your help!