Duplicate constituent matching identifies new records that may already exist in the database based on a certain percentage of data in existing fields matching. If multiple organizations exist in the same building, they will have the same address, city, state and ZIP, but a different constituent name. When this happens, and a new constituent is added that's in the same building, the only thing that does not match is the organization name - this shows up as a potential duplicate, with a match percentage of 77%.
Download and install the latest patch, which contains all fixes from previous patches. If you are running an older version, download and install the latest version and then the patch.