Can you pm a login to check it out? And what browser are you using. My guess there is some javascript on the page that was either added or from another modification that is interfering with it.
My apologies for a false alarm, I tried to make a calendar entry and had the same problem, checked it with IE and no problem, shut everything down and rebooted machine.
Problem with Firefox and editing had went away.
Shades of Windows 3.1 when you had to reboot every 12 hours
jayr