Seeing the steps you have done, did you also delete the DLC first, and whatever else you can, before clearing cache etc? Here is a post about another game and was listed as a fix. Again, seems you have done most of that. Anyway, hope it helps. Yes, that Twitter account is answered, took about 24 hours for me, and they will get back to you.
*****Fix listed for another game DLC issue******
There seems to be an issue with some of the content we released prior to release of Resident Evil 5: Gold Edition. To resolve this issue please follow the instructions below.
1. Delete any DLC that you might have downloaded separately like the free figures and Versus mode. Both of these are already included with the bundle.
2. Next Go to the system blade and then select memory. Press Y on the HDD symbol and select Clear Cache Memory.
3. Start game from HDD or disc and everything should run.
*Note* Make sure you are connected to Xbox Live.