WoFNuLL

Simple Problem, PHPBB trys to parse the BB Codes from WP, unknown Commands will lead to this error ( since the Post is not included via the post.php which filters such errors ). So just include autopostings in your Forums JUST without the shortcodes in the blog Entry ??

Seems like the Problem is a wrong Checkup from WP MU Plugin Directory

Since the Plugin works fine under / dir
but not under Created MU Sites /nulli in this case, i checked some of the Code, after replacing the plugin_dir_path($wacpath) with the Hardcoded path to the plugin Dir, it Created files in the Cache dir directly but it did not pull the pictures from there any further.

instead of pulling the pictures out of /wp-content/plugins/wow-armory-character/cache it tryed to pull the picture out of nulli(or which MU site is active)/wp-content/plugins/wow-armory-character/cache

Hope this helps to fix the Problem with the addon.