I wanted to migrate a VM from one server to the other using XenMotion when I ran into a small issue:

"This operation cannot be performed because HA would no longer be guaranteed for this pool.  To perform this operation anyway, you must disable or reconfigure HA."

Reason why this happened: When HA is enabled and a VM HA Protection level is set to Protected, in addition, the destination server must have the available memory needed to migrate the VM using XenMotion. The host server that is still holding the memory of the VM also must have that same amount of memory available (in reserve) to perform the migration. In other words, the host server must have available the same amount of memory that the VM is about to release.

Here is how to fix it the issue.

1. On the pool master host,  type: "xe pool-list" to obtain the pool UUID, in my case it is: cbfdcdfd-b7ad-2d22-3efb-6fb3945f2e92.
2. Run "xe pool-param-list uuid=[UUID]" to determine what the current setting for "ha-allow-overcommit" parameter is set to.
3. To change the overcommit setting run: "xe pool-param-set ha-allow-overcommit=true uuid=[UUID]".
4. Now run "xe pool-param-list uuid=[UUID]" and make sure that "ha-allow-overcommit ( RW): true" is set.

Now I'm able to migrate the VM from one server to the other. I live to learn more another day, Sweet!