Hi,
I'm running Windows 8 Enterprise and have the same issue. I've found ESXi 5 and IE 10 are not completely compatable yet. It appears to be an IE 10 plug-in.
By chance, I tried VMware Workstation and can access the console of each vm.
I have not looked lately to see if there is an update to ESXi 5, but would think if there is an update, that will fix the issue. At the time I upgraded to Win 8 Ent, ESXi 5 had only been out a few weeks.
I'll check and see if there is an update and try it out and get back to this post.
My pc has the latest .NET and all Windows updates to date. Only my ESXi 5 Essentials and Standard servers have the issue, we have servers with ESXi 4 Enterprise, ESXi 4.1 Standard and 5 Standard and Essentials.
Andy