Easy workaround: switch the pool protocol to RDP.
Longer workaround: it means that something in your environment doesn't like PCoIP. Here is the short list of things to look at:
1. Firewall ports on client, security server, external firewall, internal firewall. Are all the right ports (specifically UDP/TCP 4172) open?
2. Does the VM have enough video memory and/or is the resolution big enough (1280 x 800 is minimum I believe).
When you connect how long does it stay black before it disconnects? Does it disconnect?
Edited to add: Oh.. and this thread probably should be in the VMware Horizon View section and not the vCenter section.