The response you've posted by itself isn't enough information for me to determine the cause. Could you please provide the following:
Does the plugin compile successfully when loaded? Please check your server console for any compilation errors.
Are you running Oxide/uMod or Carbon?
Do you have any of the plugins listed as incompatible in the documentation installed?
What map are you using (procedural, custom, etc.)?
What steps are you taking when the error occurs?
The message "Failed to create agent because it is not close enough to the NavMesh" is generally related to NPC navigation and can be caused by map issues, spawn locations, npc plugins, or other environmental factors. I'll be happy to investigate further once I have the information above.
Additionally If you had any of those first 2 plugins installed & did not remove them prior to trying to install Console Spam Cleaner.
Then it's possible you've already messed it up. If that's the case, please stop the server remove the plugins and then install Console Spam Cleaner and boot the server as normal.