This is the error I see when looking into debug.log
ERROR: CTransaction::CheckTransaction() : coinbase script size is invalid
ERROR: CheckBlock() : CheckTransaction failed
What? But I want the script size to be valid!
Can you post the actual genesis block here (from gettransaction)?
The error implies that there is something wrong with the length of the signature. Either it does not
exist, or it is too long. The latter might be the case if your choice of the human-readable timestamp
string is something huge