I am attempting to track down a problem on my site.
I turned on maximal reporting in joomla config
I got back
Notice: Undefined variable: mosConfig_lang in /home/sites/mysite/public_html/plugins/content/jwsigpro.php on line 74

line 74 is:

$jfsupport = $pluginParams->get('jfsupport', 0); $language = ($jfsupport)?$mosConfig_lang:$language_set;

I have J1.5.8 and Joomfish on board

What does this mean?

The file-name jwsigpro.php indicates you're using SIGpro, not SIG. There's an own forum to each version. You may want to post your question there .