When I try to update software such as pages, etc. this error message comes up: There was an error in the App Store. Please try again later. (20)

Hello almauck,

Thank you for the details of the issue you are experiencing when trying to update Pages on my iMac.

I recommend signing out of the App Store and signing back in and then trying the update again:

Sign out

Choose Store > Sign Out.

Sign in using an Apple ID

1. Choose Store > Sign In, or click Sign In in the Quick Links section. The Quick Links section is located in the right part of the window shown when you click Featured, Top Charts, or Categories in the toolbar.
2. Enter your Apple ID and password, and then click Sign In.

Mac App Store: Sign in and out

http://support.apple.com/kb/PH11499

Thank you for using Apple Support Communities.

Best,

Sheila M.

Worked like a champ. Thank you!!!