these are all vcenters, multiple versions (4.1, 5.0 and 5.1)

its really odd that i can use Get-VM on the same server that it claimed disconnection with no errors, something like this:

1) Connected to 3 vCenters: vc01, vc02 and vc03

2) Run script and i get the error 'vc01 is not connected'

3) Get-VM vm01 (which happens to be at 'vc01', that just disconnected) and it retrieves it normally

edit:

ran the command with the modifications to troubleshoot disconnection like you said, and no disconnections at all ! All the 15 vCenters still connected while running the command

The exception is below

Get-VIObjectByVIView : 25/09/2013 11:25:27    Get-VIObjectByVIView        Server XXXXX is not connected.