Possible Cause: Duplicated PHP in block or node body

Possible Cause: Duplicated PHP in block or node body
In this case, PHP code may have been inserted into the body of a block, or is contained in a node's "body" field. This code declares the function in question more than once, producing the conflict. For example,

Fatal error: Cannot redeclare getnodecount() (previously declared in /var/www/sites/site.org/htdocs/includes/common.inc(1685) : eval()'d code:3) in /var/www/sites/site.org/htdocs/includes/common.inc(1685) : eval()'d code on line 9

Fix:
You can search your node_revisions table for the node IDs containing the offending code with something like:

Then examine those nodes through Drupal's administrative interface, ensuring that each function is declared in only one place.