I was having this problem in IE7 where the saturdays appear to be missing from the calendar. It displays fine in Firefox and a few people have suggested that it could be my other stylesheets messing it up so i am now using a custom calendar CSS theme and i'm still having the same problem.
Any ideas? is there a known bug with the ajax toolkit pack that is used?
If anyone else has this problem then i recommend setting a wildcard css element at the beginning of your style to blank out all posible padding and margin issues.
This fixes the problem in IE6.IE7 and firefox works fine too.
.yourCalendarTheme * {padding:0px;margin:0px;}