Error with Calendar trying to sync

I have just tried to download a Stanza calendar into my EM Client calendar. Initially it seemed ok then the entries disappeared and now I get a red triangle and an error message saying that ‘Connection failed. An attempt to connect to xxxxxxxxxxxxxxxx.yahoo.com failed. This could be caused by temporary server availability or incorrect settings.’

This the start of the listings in the Error Log section if it helps.

14:48:36 xxxxxxxxxxxxxx@yahoo.com [CalDAV] MailClient.Accounts.ConnectionException: Invalid character in the given encoding. Line 2484, position 75.
—> System.Xml.XmlException: Invalid character in the given encoding. Line 2484, position 75.
at System.Xml.XmlTextReaderImpl.Throw(Exception e)
at System.Xml.XmlTextReaderImpl.Throw(String res, String arg)

How can I get rid of this please. If not how can I remove the Stanza calendar which would seem to be the issue.

Thanks