Vista - Script producing ""Not enough storage is available to complete..."

My vbscript is producing the error ""Not enough storage is available to
complete this operation" when it connects to another server in the same
domain to enumerate disks and check free disk space.
The subroutine (incuded below) works for other servers, but not the same 2
every time it runs.
How do I troubleshoot/fix this?

Sub DisplayExchangeKVSBladesFreeSpace(strServerName)
Const HARD_DISK = 3
Dim objWMIService, colDisks, objDisk
Dim ActualFreeSpaceGb

on error resume next

Set objWMIService = GetObject("winmgmts:" &
"{impersonationLevel=impersonate}!\\" & strServerName & "\root\cimv2")

Set colDisks = objWMIService.ExecQuery ("Select * from Win32_LogicalDisk
Where DriveType = " & HARD_DISK & "")

wscript.echo " Free disk space on " & ucase(strServerName)
wscript.echo
wscript.echo " Minimum"
wscript.echo "Drive Free space allowed"
wscript.echo "-------------------------------"

For Each objDisk In colDisks
strWarning = ""
ActualFreeSpaceGb = objDisk.FreeSpace/1073741824

wscript.echo objDisk.DeviceID & vbtab &
formatnumber(ActualFreeSpaceGb,2,,,-2) & " Gb" &
space(16-len(formatnumber(ActualFreeSpaceGb,2,,,-2) & " Gb"))

Next
End Sub

Thanks for any help.

Iain