Wierd Error on Join

Hello , our users are seeing this wired error message on join , i have no clue could any one help please .

please see attachment error image

any help ?

We will most likely need a URL to your site.

I cannot find any reference to that code anywhere within dolphin.

Deano , thanks for the reply , but what making it more interesting is that its not happening all the time , so far we have 50 users registered on our web site and 2 of them noticed this issue  , I have tried to locate this code also but couldn't find either , any idea ?

as deano said, we will need the site address.