I have the exact same problem in a number of servers running Xenserver 6.1 .
OMSA 7.2 runs without a probplem, however both 7.3 and 7.3.2 that i tried fail to login .
IF i dont check the "ignore certificates" checkbox, then i get a "login failure.certificate error"
if however i check it then i get "login failure.internal error".
I checked in xenserver CLI and all services are running....