MacOS – Work Mac and home PC with same Apple ID causing problems

SnowLeopard was the first version of OS X to have built-in support for Exchange 2007. Lion Mail officially added support for Exchange 2010 (according to the Lion Wikipedia page). If the Exchange server is running Exchange 2010, it's possible that contacts and calendars were compatible enough on Snow Leopard to just work, but Mail was not.

This is genuinely because of multiple iCloud accounts used on one PC. Just for the sake of experiment, try installing iCloud on a PC where no other iCloud have ever been installed. I am sure, it will sync with it, and it is certainly a cache problem.

Secondly, regarding the My Photo Stream not showing up anything but you can still see 3 photos when you click open folder ... this is because Photo Stream shows photos when its a collection or multiple of 5 photos (e.g 5, 10, 15, 20), so if you have 5 photos in the folder, it will show up, then it won't show until it get 10 (in case of total photos <> multiple of 5, it will come up with all photos it has, as the last photo will tell that this is the end of the album). Make sure it is not a network drive, as iCloud doesn't re-download photos once it is interrupted.