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?
here's a solution:
.cal_Theme1 .ajax__calendar_days td { padding:0px; }