Hello Mario,
Is that a WIRIS editor you are using to insert an expression? The TeX notation filter or MathJax filter will work on and intranet as long as LaTeX or MathJax are installed and configured on the Moodle server. However WIRIS plugins require a connection to a WIRIS server. So normally you need internet to use them.
You should probably test the Atto equation editor to debug the filters. If you need TinyMCE support you may try TinyMCE Mathslate as an alternative to WIRIS.
Is that a WIRIS editor you are using to insert an expression? The TeX notation filter or MathJax filter will work on and intranet as long as LaTeX or MathJax are installed and configured on the Moodle server. However WIRIS plugins require a connection to a WIRIS server. So normally you need internet to use them.
You should probably test the Atto equation editor to debug the filters. If you need TinyMCE support you may try TinyMCE Mathslate as an alternative to WIRIS.