You should locate the inputs.conf that has this input and apply a blacklist there. More information about blacklists for inputs is available in the following links:
http://docs.splunk.com/Documentation/Splunk/5.0.2/Data/Whitelistorblacklistspecificincomingdata
http://docs.splunk.com/Splexicon:Blacklist
http://docs.splunk.com/Documentation/Splunk/5.0.2/Admin/Inputsconf