We are aware of the unclear message that says, "Your inventory is full. Clear more space in your override me inventory."
We apologize for the poor language in that message. There is no 'override me' inventory. The inventory section that is full is your Social Items.
Although it doesn't have a fullness indicator, there is a limit of 24 stacks of Social Items in your inventory.
To clear space in the Social Items tab, go into the 'Misc' tab (the farthest right tab), and the first area is the social items category.
You will need to delete some full stacks of items in order to free up an empty slot in the social items area.
This may mean you need to make some difficult decisions about what building you want to upgrade first, and put off upgrades of others.
The confusing message will be changed very shortly. We hope this clears up the issue for you.
--The Mafia Wars 2 Support Team