I don't yet have a solution, but I am seeing the same problem with the same errors in my logs, View 5.1.2, both 4.6 and 5.1.1 agents, Windows XP, ESXi 5, on a LAN. My users are reporting that it occurs when they have several applications open at once. The relevant part of my logs is below:
02/28/2013, 09:34:45.406> LVL:1 RC: 0 MGMT_PCOIP_DATA :BW: Decrease (overrun) old = 289.2762 new = 85.4560, old plat = 201.7952, current=135.144, avg=109
02/28/2013, 09:34:45.500> LVL:1 RC: 0 MGMT_PCOIP_DATA :BW: Decrease (loss) old = 85.4560 new = 73.2785
02/28/2013, 09:34:45.500> LVL:2 RC: 0 MGMT_IMG :rcv nak 2 seq_id 172 disp 0 fsp 4 f_ref 214
02/28/2013, 09:34:45.500> LVL:2 RC: 0 MGMT_IMG :SW_HOST_IPC: NAK for fsp 4 seq 214. (ref id=37) Ack ref available, recode from input
02/28/2013, 09:34:45.531> LVL:2 RC: 0 MGMT_IMG :SW_HOST_IPC: IPLP: recode from input: fsp=4 refvld=1 seq=216
02/28/2013, 09:34:46.125> LVL:1 RC: 0 MGMT_PCOIP_DATA :BW: Decrease (loss) old = 112.5000 new = 96.4688
02/28/2013, 09:34:46.125> LVL:2 RC: 0 MGMT_IMG :rcv nak 2 seq_id 185 disp 0 fsp 4 f_ref 215
02/28/2013, 09:34:46.125> LVL:2 RC: 0 MGMT_IMG :SW_HOST_IPC: Encoder clearing recode for fsp 4 seq 216 (ref id=88)
02/28/2013, 09:34:49.828> LVL:2 RC: 0 MGMT_SSIG :Session closed remotely by peer (192.168.7.69, 00-80-64-86-3C-7D, PRI: 0)
02/28/2013, 09:34:49.828> LVL:2 RC: 0 MGMT_SSIG :Received from peer: BYE disconnect reason cause (0x400)
02/28/2013, 09:34:49.828> LVL:2 RC: 0 MGMT_SSIG :Session closure reason cause (device:internal: SSIG keepalive failure)
02/28/2013, 09:34:49.937> LVL:1 RC: 0 MGMT_PCOIP_DATA :BW: Decrease (loss) old = 114.4877 new = 182.6912
02/28/2013, 09:34:49.937> LVL:2 RC: 0 MGMT_IMG :rcv nak 2 seq_id 247 disp 0 fsp 10 f_ref 52
02/28/2013, 09:34:49.937> LVL:2 RC: 0 MGMT_IMG :SW_HOST_IPC: NAK for fsp 10 seq 52. (ref id=2) Ack ref available, recode from input
02/28/2013, 09:34:49.937> LVL:2 RC: 0 MGMT_IMG :rcv nak 2 seq_id 248 disp 0 fsp 11 f_ref 2
02/28/2013, 09:34:49.937> LVL:2 RC: 0 MGMT_IMG :SW_HOST_IPC: NAK for fsp 11 seq 2. (ref id=75) Ack ref available, recode from input
02/28/2013, 09:34:49.937> LVL:2 RC: 0 MGMT_IMG :rcv nak 3 seq_id 250 disp 0 fsp 10 f_ref 53
02/28/2013, 09:34:49.937> LVL:2 RC: 0 MGMT_IMG :rcv nak 3 seq_id 251 disp 0 fsp 11 f_ref 3
02/28/2013, 09:34:50.031> LVL:2 RC: 0 MGMT_IMG :SW_HOST_IPC: IPLP: recode from input: fsp=10 refvld=1 seq=62
02/28/2013, 09:34:50.031> LVL:2 RC: 0 MGMT_IMG :SW_HOST_IPC: IPLP: recode from input: fsp=11 refvld=1 seq=13
02/28/2013, 09:34:50.296> LVL:2 RC: 0 MGMT_IMG :Resetting encoder (reset_type=0)
02/28/2013, 09:34:50.296> LVL:2 RC: 0 MGMT_PCOIP_DATA :mgmt_pcoip_data_set_media_activation: URBoIP is used. OHCI & EHCI media channel is turned OFF
02/28/2013, 09:34:50.296> LVL:1 RC:-500 VGMAC :tera_sock_recv() failed - Interrupted system call (10004)!
02/28/2013, 09:34:50.296> LVL:2 RC: 0 VGMAC :PCoIP UDP RX thread exiting
02/28/2013, 09:34:50.296> LVL:1 RC:-500 MGMT_PCOIP_DATA :INIT: Peer has reset our PCoIP connection. Aborting session ...
02/28/2013, 09:34:50.296> LVL:2 RC: 0 MGMT_VCHAN :app_reset: Session has been dropped. Forcing all channels to close!
02/28/2013, 09:34:50.296> LVL:1 RC: 0 MGMT_DDC :mgmt_ddc_fcc_callback: queuing TERA_MGMT_FCC_EVENT_RESET [pri=0]
02/28/2013, 09:34:51.296> LVL:0 RC: 0 IMG_FRONTEND :close_displays: reset SVGADevTap.
02/28/2013, 09:34:51.296> LVL:2 RC: 0 MGMT_IMG :CODEC: State change from CODEC_RUNNING to CODEC_DISABLED
02/28/2013, 09:34:51.296> LVL:2 RC: 0 COMMON :TERA_PCOIP: SESSION_EVENT=TERA_MGMT_SYS_SESS_EVENT_CLOSED, disconnect cause (0x400)
02/28/2013, 09:34:51.296> LVL:2 RC: 0 SERVER :server main: cb_notify_session_status called 20 with tera_disconnect_cause(0x400)
02/28/2013, 09:34:51.296> LVL:2 RC: 0 SERVER :server main: TERA_MGMT_SYS_SESS_EVENT_CLOSED with disconnect cause (0x400).
02/28/2013, 09:34:51.296> LVL:1 RC: 0 SERVER :map_tera_to_agent_close_code: TERA_DISCONNECT_CAUSE_DEVICE_INTERNAL_SSIG_KEEPALIVE_FAILURE -> PCOIP_AGENT_CLOSE_CODE_NETWORK_INTERRUPTION
02/28/2013, 09:34:51.296> LVL:2 RC: 0 SERVER :connection_closed: code = 3.
02/28/2013, 09:34:51.296> LVL:1 RC: 0 VGMAC :Session stats: Average TX=0.112354 average RX=0.00894231 (Mbps) Loss=1.75%/0.71% (R/T)
02/28/2013, 09:34:51.296> LVL:2 RC: 0 MGMT_SYS :Session closed remotely!
02/28/2013, 09:34:51.296> LVL:2 RC: 0 MGMT_SYS :********************************************************
02/28/2013, 09:34:51.296> LVL:2 RC: 0 MGMT_SYS :********************************************************
02/28/2013, 09:34:51.296> LVL:2 RC: 0 MGMT_SYS :********************************************************
02/28/2013, 09:34:51.296> LVL:2 RC: 0 MGMT_SYS :********************************************************
02/28/2013, 09:34:51.296> LVL:2 RC: 0 SERVER :server mailbox: MBX_SHUTDOWN with agent disconnect reason code (0x0)
02/28/2013, 09:34:51.296> LVL:2 RC: 0 SERVER :server mailbox: Stopping mailbox message loop
02/28/2013, 09:34:51.296> LVL:2 RC: 0 SERVER :server main: exiting
02/28/2013, 09:34:51.296> LVL:2 RC: 0 SERVER :server cleanup: tearing down pcoip with agent disconnect reason code(0) and waiting
02/28/2013, 09:34:51.296> LVL:1 RC: 0 SERVER :map_agent_to_tera: DISCONNECT_GENERIC -> TERA_DISCONNECT_CAUSE_HOST_BROKER_GENERIC
02/28/2013, 09:34:51.296> LVL:2 RC:10038 PERF :tera_perf_monitor_send: Failure during message write (header).
02/28/2013, 09:34:51.296> LVL:1 RC:-500 PERF :tera_perf_unregister: Sending remove_instance failed.
02/28/2013, 09:34:51.296> LVL:0 RC: 0 MGMT_SESS :Tearing down the session
02/28/2013, 09:34:51.296> LVL:2 RC: 0 MGMT_VCHAN :VChanPluginExit: Closing plugin 'VMware_Server'.
02/28/2013, 09:34:51.343> LVL:2 RC: 0 MGMT_VCHAN :VChanPluginExit: Plugin 'VMware_Server' is closed.
02/28/2013, 09:34:51.343> LVL:2 RC: 0 MGMT_VCHAN :VChanPluginExit: Closing plugin 'mksvchanserver'.
02/28/2013, 09:34:51.343> LVL:2 RC: 0 MGMT_VCHAN :VChanPluginExit: Plugin 'mksvchanserver' is closed.
02/28/2013, 09:34:51.343> LVL:1 RC: 0 MGMT_VCHAN :=> Successfully exited all the VChan plugins
02/28/2013, 09:34:51.343> LVL:2 RC: 0 SERVER :server cleanup: detaching inputdevtap
02/28/2013, 09:34:51.343> LVL:2 RC: 0 SERVER :server cleanup: closing mailboxes
02/28/2013, 09:34:51.343> LVL:2 RC: 0 SERVER :server cleanup: freeing argument copy
I will keep you posted as I troubleshoot.