When simulating a problem on a ClusterXL cluster with the command "cphaprob -d STOP -s problem -t 0 register" to initiate a failover on an active cluster member, you can use the command "cphaprob -d STOP unregister" to remove the problematic state and return the cluster to normal operation.
Option A correctly identifies the command that allows you to remove the problematic state, making it the verified answer.

Explanation
To manually failover a cluster during a zero-downtime upgrade, you can use the command clusterXL_admin down on the active cluster member. This command will gracefully change the state of the cluster member to down and trigger a failover to the standby cluster member. This way, you can upgrade the cluster member that is now down without affecting the traffic processed by the other cluster member. You can then use the command clusterXL_admin up to bring the upgraded cluster member back online and repeat the process for the other cluster member. This command is useful for testing and debugging purposes and does not survive reboot unless you add the -p option or use the set cluster member admin down/up permanent command in clish1. The other commands are not valid for initiating a manual failover. The set cluster member down command is used to remove a cluster member from a cluster. The cpstop command is used to stop all Check Point services on a gateway. The set clusterXL down command does not exist.

Explanation
Mobile Access is not part of the SandBlast component. Mobile Access is a software blade that provides secure remote access to corporate resources from various devices, such as smartphones, tablets, and laptops. Mobile Access supports different connectivity methods, such as SSL VPN, IPsec VPN, and Mobile Enterprise Application Store (MEAS). Mobile Access also integrates with Mobile Threat Prevention (MTP) to protect mobile devices from malware and network attacks. References: Check Point Security Expert R81 Course, Mobile Access Administration Guide, SandBlast Mobile Datasheet