The restrictions on how often the guide can be updated have recently changed.
They are now set to be once every hour for the channels list and also once every hour for the guide itself (these are two separate requests). There is also a limit on how often remote scheduling requests can be made, this is set to once every 15 minutes, any attempts within 15 minutes of the last successful request will return an error in EyeTV saying that there is a problem with the username or password (unfortunately EyeTV does not handle the actual error message correctly).
If you try again by going through the program guide screen, and then selecting the 'gear' icon at the top of the screen and then select “Update IceTV Guide” it should then update the guide (as long it has been over one hour since the last attempt).
One thing that we have found is that when going into the preferences window it will do a channels list request so that when it tries to download the guide after that (using the Update now) button it will fail to download as it has been within the hour.
There is also a new 'blacklisting' that could be affecting you, please see the post regarding an Important IceTV Service Announcement.