Symptom
.Mac will not function properly if the Internet System Preferences are not set up properly.
Solution
Mac OS X contains several features that are tightly integrated with .Mac, Apple's suite of Internet services. To use services such as iDisk access from the Finder, the Internet System Preferences need to be set up properly.
Configuring the Internet System Preferences
1. Open System Preferences.
2. Click Internet to reveal that pane.
3. Click the .Mac tab to select it (unless it is already visible)
4. Enter your .Mac user name and password.
If you do not yet have a .Mac account, either full or trial, you can create one by clicking Sign Up.
Selecting your .Mac email account as your default email account
1. Click the Email tab.
2. Click the checkbox to enable the "Use iTools Email account" feature. The proper email settings are automatically entered into the appropriate boxes.