Limitations / Disadvantages of Black-box testing
Without clear and concise specifications of software components, black box test suites are hard, if not impossible, to develop. Because proper documentation is often still lacking, black box testing cannot be applied in some software projects.[Source]
When using black box testing, the tester can never be sure of how much of the SUT has been tested. No matter how clever or diligent the tester, some execution paths may never be exercised. [Source]
Impossibility of testing the quality of coding and its strict adherence to the coding standards. [Source]
Also see:
Black-box Testing
Advantages of Black-box Testing
Exhaustive Testing