intermittent connectivity drop

[Scots1]

I have looked through the forum, but have been unable to find any similar issues. I apologise if I have missed something.

I have the following setup -

Cisco ASA5505 -> 3Com 2924 Switch -> ESX3i

The ESX box has the following specs - 2xquad 2.5Ghz CPU's, 16GB RAM, 4xIntel GB NIC's and 2xIntel GB NIC's onboard. UT has 1x vCPU @2.5Ghz, 2GB memory, 40GB disk and 2 network adaptors assigned.
UT was installed from an ISO (6.1x) and upgraded to 6.2. I am currently downloading the 6.2 ISO and will try another clean install.

I have the following vSwitches configured on ESX
vSwitch0 - Management Network (multiple NIC's assigned)
vSwitch1 - Internal (No NIC's assigned)
vSwitch2 - External (Multiple NIC's assigned)

vSwitch1 and vSwitch2 are both set to promiscuous mode - accept.

UT is running in bridged mode with public IP on external and internal bridged to external. Intrusion detection, attack blocker, firewall and reports are loaded in the rack.
The idea being that all other VM's on host will be on the internal switch i.e. behind UT, however when I move a system onto the internal switch connectivity drops intermittently for no apparent reason. I have been unable to match up the outages with any events logged and outages continue even if all modules in the rack are switched off.

Any ideas, suggestions help would be hugely appreciated

Thanks

Initially got the same result with 6.2 ISO, intermittent loss of connection to internal, downloaded iso again and setup another clean install. All running smoothly.