Setup Failure Codes/PHP iconv support
The page identifies a minor configuration problem. Some functionality may be impacted but most parts of DAViCal should work fine.
The CalDAV protocol requires all communication to be in the UTF-8 character set. This is a Good Thing(tm), but sadly the real world often dwells in some weird mix of ISO-8859-15, Windows-1252 or BIG-5.
The "iconv" support in PHP allows us to at least *try* to translate between them.
Quite possibly DAViCal will work without this. Except when it doesn't. We recommend you have it available.