What version of code and what model of SRX do you have?
1454 is a "Failed to recieve HTTP response" error and the only time I've seen it was right after Pulse was sold by Juniper. Most version of codes released after that date had problems after the client software was removed from the SRX. This was resolved in the following maintenance releases:
- Junos 12.1X44-D60
- Junos 12.1X46-D45
- Junos 12.1X47-D35
- Junos 12.3X48-D25
See TSB16860 for more details. Assuming that your loopback is reachable externally and that you have the appropriate policies and host-inbound-traffic system services enabled this should resolve your problem.