amazon ec2 - ec2-consistent-snapshot volume does not exist?

Does anybody know why this might happen?

me@ip-10-176-234-62:/$ ec2-describe-volumes
VOLUME  vol-994ec1fd    8   snap-2971f04d   us-west-1a  in-use  2012-05-14T18:57:01+0000

ATTACHMENT  vol-994ec1fd    i-a49a2ae2  /dev/sda1   attached    2012-08-31T18:39:18+0000

me@ip-10-176-234-62:/$ ec2-consistent-snapshot vol-994ec1fd --aws-access-key-id xxxx --aws-secret-access-key xxxxx
    ec2-consistent-snapshot: ERROR: The volume 'vol-994ec1fd' does not exist.

Answer

Try to specify the region on the command-line, e.g.:

--region us-west-1a