I've compiled a version of geth where I modified CalcDifficulty() in core/block_validator.go to make mining difficulty constant, see reference. Starting up the private chain, creating accounts and mining works fine.
If I try via the javascript console to unlock an account, it works, and returns true.
personal.unlockAccount(eth.accounts[0])
But when I try to send a transaction:
personal.sendTransaction({from:eth.accounts[0], to: eth.accounts[1], value: 20000000})
I get the following:
Error: could not decrypt key with given passphrase
at web3.js:3104:20
at web3.js:6191:15
at web3.js:5004:36
at <anonymous>:1:1