Reports have surfaced that iCal calendar events that contain all-day events are having issues when publishing to MobileMe. The issues appear to be related to Snow Leopard's version of iCal. Apple is aware of the issue and is currently working on a fix. In the meantime, several users offer suggestions for workarounds with mixed results.
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.