I have installed the newest version of Freichat in a Joomla! 2.5.14 version, but in the window's chat, don't load user list say some thing like "Loading User, list, querying data base".

Looking Google Crhome's debug mode I found this error:

GET http://glmarquitectura.com.mx/freichat/server/freichat.php?freimode=getmemb…%5B%5D=&custom_mesg=Disponible&long_poll=false&in_room=-1&custom_gst_name= 500 (Internal Server Error) jquery-1.5.min.js:16
send jquery-1.5.min.js:16
d.extend.ajax jquery-1.5.min.js:16
d.(anonymous function) jquery-1.5.min.js:16
d.extend.getJSON jquery-1.5.min.js:16
FreiChat.get_messages main.php?id=85a71fa5291cc24028841d567629c106&xhash=934de9a8d64ccc80a1968673543e1020:1271
FreiChat.yourfunction main.php?id=85a71fa5291cc24028841d567629c106&xhash=934de9a8d64ccc80a1968673543e1020:1230
loopme main.php?id=85a71fa5291cc24028841d567629c106&xhash=934de9a8d64ccc80a1968673543e1020:1226

Some Idea?

Try this,

Go to your website, open developer tools(f12) in chrome .
Click on network tab , click on any request made by freichat , then click on response for that request .

You should see some error there , post that error here.