Not able to demote Storage-domain from Master

Issue

I am trying to deactivate the current Master Storage Domain, but receiving the following error:

2015-06-04 17:06:49,961 WARN  [org.ovirt.engine.core.bll.storage.DeactivateStorageDomainWithOvfUpdateCommand] (ajp-/127.0.0.1:8702-1) [123456ab] CanDoAction of action DeactivateStorageDomainWithOvfUpdate failed for user admin@internal. Reasons: VAR__TYPE__STORAGE__DOMAIN,VAR__ACTION__DEACTIVATE,ERROR_CANNOT_DEACTIVATE_MASTER_DOMAIN_WITH_TASKS_ON_POOL
2015-06-04 17:06:49,961 INFO  [org.ovirt.engine.core.bll.storage.DeactivateStorageDomainWithOvfUpdateCommand] (ajp-/127.0.0.1:8702-1) [123456ab] Lock freed to object EngineLock [exclusiveLocks= key: 00000002-0002-0002-0002-000000000303 value: POOL
key: 7c367a8b-8acb-42dc-9805-42c92a123456 value: STORAGE
, sharedLocks= ]