fatal: reference is not a tree

otubo@vader ~/develop/ock/dev/icsf_tools master $ ./bootstrap.sh
Submodule 'ock' (https://github.com/joylatten/opencryptoki.git) registered for path 'ock'
Cloning into 'ock'...
remote: Counting objects: 8279, done.
remote: Compressing objects: 100% (2957/2957), done.
remote: Total 8279 (delta 5315), reused 8229 (delta 5276)
Receiving objects: 100% (8279/8279), 3.40 MiB | 937 KiB/s, done.
Resolving deltas: 100% (5315/5315), done.
fatal: reference is not a tree: 6e0b6765d1bebeec658d314cc09a10b7bdbbff3f
Unable to checkout '6e0b6765d1bebeec658d314cc09a10b7bdbbff3f' in submodule path 'ock'