Strangest thing – while syncing a dialog kept opening and asking for the password of my Mac, and the drop down showed that it was a kcsync issue. I’d enter the password, that the Mac accepted, but it wouldn’t sync the Keychain. Everything else was syncing fine, but not the Keychain.
Googling the forums LarryMcJ on the macosx.com forum provided the answer. From terminal enter the following to reset the Keychain password. Worked like a charm.
/System/Library/Frameworks/SecurityFoundation.framework/Versions/A/Resources/kcSync.app/Contents/MacOS/kcSync -reset

Problem syncing Keychains to .Mac 










Update for Snow Leopard (10.6) the path has changed (slightly) and now you’ll need to enter
/System/Library/Frameworks/SecurityFoundation.framework/Versions/A/kcSync.app/Contents/MacOS/kcSync -reset