Welcome to the Forum!
i believe you may need the 580EX II or 430EX II for compatability with the 5D MarkII. I believe the flash synch speed for the 5D MarkII is 1/200s. You should have a custom function to allow you to set it. I don't know if this would allow it to synch with the 580EX or not. I set the synch speed on my 30D to 1/250s to work with the 580EX.
BTW, when you were changing the flash settings, did you have the flash attached? If not, you will get an error message.