Fatal error: Class 'Browser' not found : After Updating drupal 6.20 to 6.26
The error message says eval()'d code on line 4. You have a PHP block, node or something similar that tries to include a file called Browser.php. That is not a file supplied with Drupal core. What you can do... just before line 1731 add something like if(strpos($code, 'Browser.php')) { file_put_contents('/tmp/log', print_r(debug_backtrace(), TRUE)); exit;} and then study the log to see where it's called from to figure it out. If it's called from block, the backtrace will contain the module and delta, if it's a node, the nid will be there and so on.