"I already have v1.37 firmware, which is the latest."
Correct, but a force update can ensure that we aren't having any software inconsistancies (like with the interface). Unfortunately I am not finding a way to set it up through the NASNAVI (though I hardly ever use it).
I would also heed Davo's advise. Simply trying a different browser and/or computer can tell you much about where the problem lies. It could be flash or a configuration for all we know.
Simple sounding solutions can often be the correct ones