It is not guaranteed that setting or revoking the maintenance mode is successful at all times. If you set the SAP HA Maintenance Mode for all instances with SAP methods, this can fail in the following cases:
An instance is not fully up and running. You will receive an error message from SAP, but this message does not include the instance number nor the resource group, so you will have to check manually for which instance the command failed.
The Oracle Solaris Cluster resource group which contains the instance is undergoing a reconfiguration. You will receive an error message from SAP, but this message does not include the instance number nor the resource group, so you will have to check manually for which instance and resource group the command failed.
At the moment SAP contacts the sapstartsrv process of an instance to start the maintenance process for this instance, the sapstartsrv does not run or does not respond. In this case the instance is skipped, no maintenance action is done and you do not see an error message.
You must check manually if the SAP HA Maintenance Mode was set or revoked for all instances.