Setup Failure Codes/PHP Magic Quotes GPC off
The page identifies a major configuration problem. DAViCal might appear to work somewhat but major functionality will be broken until this is resolved.
In it's day PHP has had some really, *amazingly* bad misfeatures, and this was one.
This "feature" takes all of the incoming data and puts a backslash in front of every ", ' or backslash. Like "magic". Supposedly this makes it easy to ignore the content of the data and stick it into a database.
If you've ever seen backslashes quoted back at you in a website the likely cause is this. If you want to see lots of backslashes in your text then by all means turn it on: after a few days you'll pretty much only have backslashes escaping backslashed backslashes.
Don't say we didn't warn you :-)