Apple Support Discussions user "larryhitz" reports:
I worked with MobileMe support last week and here is a C&P of my e-mail from them I will share and it DOES work for me:
At the moment, our suggested work arounds are (you guessed it!) to use the iCal publish function in 32 bit or remove repeating/all day events. Of course, our engineers are working to get things on track for 64 bit and eliminate this bug.
Pick iCal in your apps folder and COMMAND+I to get info. Click the box to run launch iCal in 32-bit mode.
A report on this issue from The Unofficial Apple Weblog says that Apple is currently aware of the issue and is working on a fix. I tested my own calendars using Snow Leopard on my MacBook Pro and was not able to replicate the issue.