Nope, you should be able to equip both (I did last night and now have both as options).
Do the following:
1) Check to make sure it hasn't already activated it (go to the naming bit and see if you have the option of Special Envoy, if you do then simply remove the item from your inventory, it's a dupelicate).
2) If that doesn't work then try re-claiming it from the C-Store and trying again (delete the current blue square first)
3) Finally if you have no luck with the above then submit a ticket in game, be sure to detail that you have tried the above to save the GMs time.
The above poster is correct. I have no trouble switching between the two titles. Although they never appeared in my inventory--not even as invisible items. They simply appeared in my titles list under the "Accolades" tab.