Went to site to do with wire shark trace . I observed that the invite were all cancelled .Issues resolved after the Draytek firmware was upgrade to the current level . Also changed the port in the 400 to Gamma 61166 to 5060 i.e.88.215.63.3:61166. to 88.215.63.3:5060 However, it worked when the software was on version 4.
Thanks