If you receive the "You have reached the limit for this item" error while trying to purchase Total Protection from the Black Market, you already have at least one such item in your possession.
The Total Protection item has a limit, and you can't buy another Item if you already have one. This limit applies to all the Total Protection items, independent of their duration.
Also, you will not be able to purchase Total Protection Items if you have Total Protection active on your Base. Please note that it is impossible to acquire any kind of Total Protection Item while your Base is already protected by one of the Protection Items.