Generating blocks in regtest: "hash doesn't match nBits" I'm getting this error in regtest mode after setgenerate RPC:


  ERROR: CheckProofOfWork() : hash doesn't match nBits


After looking for error text in src I found a match in pow.cpp (obviously standing for proof of work) with following extract from code: 

// Check proof of work matches claimed amount
if (hash &gt; bnTarget)
     return error("CheckProofOfWork() : hash doesn't match nBits");


Does it mean there's a target in regtest?If yes, isn't it contradicting to difficulty being 0?
The regtest difficulty is not 0. It is around 0.0000000005 initially (corresponding to 1 hash in 2 being valid), and retargets the same way that the main network does, every 2016 blocks.

The fact that you see this error is a bug though, which will probably be fixed in Bitcoin Core 0.11.