On installing the OAuth module in a Drupal site, this error appeared:
fatal error: class 'OAuthCommonHooks' not found in [path]

Fatal error: Class 'OAuthCommonHooks' not found in /drupal-6.13/sites/all/modules/oauth_common/oauth_common.module on line 58

Apparently you can fix it one of two ways: if the site is still working enough to get to the performance page (?q=admin/settings/performance), just hit the Clear cached data button at the bottom of the page.

If the site is down, open phpMyAdmin and find the cache table. Click Browse and delete the row with "autoload" in the cid column.

Thanks to xolotl for this tip.