Re: bbPress works alone, integration failed.
Sounds like that pm plugin is not working or not activated, but it’s still being called by the template?
It’s a good practice to call plugins like so, to prevent these sort or fatal errors if the plugin is not available:
if ( function_exists('pm_fp_link') ) {
// then call the function
}
Then there won’t be a fatal error if the plugin is not available.