I have a very similar problem, just a slightly different error:
Code
Error #0:
exception 'OMVModuleDockerException' with message 'Error: "couldn't connect to host" - Code: 7' in /usr/share/omvdocker/Utils.php:63
Stack trace:
#0 /usr/share/omvdocker/Utils.php(125): OMVModuleDockerUtil::doApiCall('http://localhos...')
#1 /usr/share/openmediavault/engined/rpc/docker.inc(145): OMVModuleDockerUtil::getImages('42005', true)
#2 [internal function]: OMVRpcServiceDocker->getImages(Array, Array)
#3 /usr/share/php/openmediavault/rpcservice.inc(125): call_user_func_array(Array, Array)
#4 /usr/share/php/openmediavault/rpc.inc(79): OMVRpcServiceAbstract->callMethod('getImages', Array, Array)
#5 /usr/sbin/omv-engined(500): OMVRpc::exec('Docker', 'getImages', Array, Array, 1)
#6 {main}
Any ideas why this is happening? I'm running fully updated OMV 2.2.8 btw.