When you have 'Automatically detect time offset' enabled in the Bookmark settings, Yummy FTP sends a temporary file to the server in order to determine the time difference. In this case, the login directory, or whichever Initial Path setting you have, does not allow writing and therefore you get an error message.
I would expect Yummy to be silent about this feature failing on the initial login and try again later, at least that is the intention, so you would never normally see such an error message. Could you send me the transcript which generates this so I can make adjustments as needed?
To fix the problem, change the Initial Path to a folder which is writable for you, or disable the 'Automatically detect time offset' option.
