I think Shelley has identified the area we need to look at, but from messing around with the link you sent me by PM, that code is definitely there and is set to 274px;
I can only assume that somewhere else, however, some padding has been applied or similar that is pushing it beyond that width.
If you change the code to:
Code:
#AccountMenu {
width: 275px;
}
It seems to display fine.