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You can follow the steps in this post to re-install. There should be no downtime on your VMs with these steps.
halizard.com/forum/suggestion-box/86-upgrade-xen-6-2-to-6-5#471

I would use this procedure as a lost resort only. Since you are able to reproduce the issue by connecting XenCenter to the pool, perhaps invest some time to see why XAPI is hanging before reinstalling everything.