Can't get the GUID of an UserGroup Object?

Hello, i am trying to retrieve the GUID of an UserGroup i have in my DB and i need to create a List with those GUIDs but nothing that i tried is working.

 I've have this to get list of user groups from my BD which:

      for (var k = 0 ; k < g_ousergroups.length ; k++ ){

        var ocurrentusergroup = g_ousergroups[k];

        var ocurrentattribute = ocurrentusergroup.Attribute(1000, g_nloc);

and i have tried to get the GUID from the current user group with:

sValue = g_ousergroups[k].Attribute(Constants.AT_ID, g_nLoc).getValue();

sValue = oObjDef.Attribute(Constants.AT_ID, g_nLoc).getValue();

sValue = g_ousergroups[k].Attribute(55, g_nLoc).getValue();

- When i check the value of the variable there is always no value at all

 and

 var auxi= g_ousergroups[k].FindGUID();

this gives me an error of "Cannot find in function FindGUID in object UserGroup object ID= ...."

Please help, i am completely stuck with this problem.

Best Regards.