If you have an AMD graphic card and you're using Firestorm viewer try to change this in the DebugSettings :
FSDisableAMDTextureMemoryCheck: Disable checking for low texture memory on AMD graphics cards
Change from FALSE to TRUE
I had same issue and it solved it.
I have the same pb. It has worked some days, and now, Merchant Ooutbox doesn't initialize with the marketplace. It's now 3 days I try desperately to find a way to make it work...