Mac App Store presenting 'unknown error 100'

A number of people are experiencing an error stating "unknown error 100" when using the new Mac App Store in OS X 10.6.6. Here are some ways to overcome this issue.

Topher Kessler MacFixIt Editor
Topher, an avid Mac user for the past 15 years, has been a contributing author to MacFixIt since the spring of 2008. One of his passions is troubleshooting Mac problems and making the best use of Macs and Apple hardware at home and in the workplace.
Topher Kessler

In addition to having some downloads pausing and hanging when users attempt to download them, the new Mac App Store is also giving users an "unknown error 100" when they attempt to navigate.

This problem is likely another "break in" issue, and so far has been addressed by users in the following ways:

  1. Restart the Mac
    Some people have found that simply restarting their computer makes this problem go away. You might try rebooting into Safe Mode and then restart normally again to have the system run a few diagnostics and cleanup routines that may also help.

  2. Sign out and sign back in
    Other users have found that a more basic approach is to just sign out of the Mac App Store and then quit the program. After doing this, open the program and sign back in again.

  3. Remove cookies
    It is possible this problem could be related to the handling of cookies. Open Safari and go to the "Security" section of its preferences. Then click the "Show Cookies" button and remove all cookies pertaining to "iTunes" or "Apple" (you can search for these), and then try the store again.

If you have any App Store tips or fixes, please let us know by e-mailing us or posting them in the comments. We look forward to hearing about your experiences.

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