The fundamental problem?
The fundamental problems are firstly that quantum phenomena are essentially statistical, so a quantum logic block might legitimately be called a "maybe gate", and secondarily that minute levels of interference ("noise") are likely to be sufficient to completely modify results. Under these circumstances error correction using additional bits suffers from diminishing returns, as the additional bits are also both statistical and subject to interference. So recursively, you might need additional bits to correct (or at least validate) the error correcting bits - ad infinitum. Consequently, as at some point we have to stop adding layers of correction, there will always be a practical limit to the consistency of results from a quantum computer.