Http Method Not Supported
From DAViCal Wiki
The DAV specification allows for an OPTIONS method which can be called for any item or collection and which will return a list of the HTTP methods which are supported for that URL.
At 0.5.0 RSCDS supports OPTIONS, GET, HEAD, PUT, DELETE, PROPFIND, REPORT, MKCALENDAR and MKCOL methods.
Client software should perform OPTIONS requests in order to identify available functionality, so this should not generally cause issues. This coverage should be expanded to the LOCK, UNLOCK and PROPPATCH methods in upcoming releases.

