Transaction still unspendable with CLTV
Bitcoin Core does not support signing scripts with CLTV instructions.

It only supports:


P2PK
P2PKH
k-of-n multisig
P2WSH wrapped versions of the above
P2WPKH
P2SH wrapped versions of the above


If you want to sign anything else, you'll need to implement your own signing logic.

The error you're seeing is due to the spending transaction not having the nLockTime field set. In general, CLTV works indirectly:


A CLTV output puts a requirement on the spending transaction to have an nLockTime field larger than the time specified by the CLTV instruction.
A transaction with a nLockTime field can only be confirmed when the blockchain time is after the value in that field (this is even the case when no CLTV is present).


But regardless, even if you did have a correct nLockTime field, signrawtransaction would still not know how to sign for that script.