Yeah its only compatible with 1.7.2 well so far at least.   Seems that a route call from the plugin to either the facebook api or the core router is wrong.   Its probably just a simple page name value in the router call. 

Ill have to download 1.7.3 and unpack it and check it out.  Ill try to get back with you asap. 

provide the screenshot of your FB app settings please

and the exact steps after which you get this error. 

when I click settings, page redirects to www.mysite.com/ INVALID_URI

and if I go www.mysite.com/admin/plugins/fbconnect/settings it is OK

Defender, I'm sorry but we cannot reproduce that on our side. 

Can you please try to deactivate/reactive plugin and try again? if the issue persists, PM me your admin details for the website and FTP access details. 

I have updated my site auto. now I have downloaded fresh 1.7.3 and fbconnect plugin to my pc.

I compared these plugins, there is diference .

in fresh oxwall 1.7.3 init.php (fbconnect) is missing code

$route = new OW_Route('fbconnect_configuration_fields', 'admin/plugins/fbconnect/settings', 'FBCONNECT_CTRL_Admin', 'settings'); // backward compatibilityOW::getRouter()->addRoute($route);

I have add it, and now all OK. Problem SOLVED

I thought it might be a route, sorry i did not get back to you i was overwhelmed yesterday with trying to get my plugin done.   So sorry about that.. 

nice job :)  thanks for letting us know

I just checked the package, downloaded brand new, and this line of code is there, something was wrong on your side, I have even checked the test websites I have. 

Anyway, thank for letting us know.