Regarding device deletion form BIG IQ device

In a BIG IQ,we add a device but it doesn't add properly into BIG IQ.In device configuration 

Configuration History =Error getting resource provisioning from /mgmt/tm/sys/provision on _HOSTNAME_ (_MANAGEMENT_IP_), message 'Network is unreachable' was returned

and 

Configuration Import =Failed to copy configuration to working-config; reason: Failed getting source subcollection objects: com.f5.rest.common.RestWorkerUriNotFoundException: URI path not registered. Please verify URI is supported and wait for /available suffix to be responsive.

this error is showing in BIG IQ device against that device.

but tried to remove that device but it doesn't show the REMOVE Device Option.

Please Suggest me to what to do ?