When using WMI to query a Win32_PerfRawData performance counter no data is returned. For example the following query against the CIMV2 provider does not return data:

Set objWMIService = GetObject("winmgmts:\" & strComputer & "\root\CIMV2")
Set colItems = objWMIService.ExecQuery("SELECT * FROM Win32_PerfRawData_CitrixICA_ICASession", "WQL", wbemFlagReturnImmediately + wbemFlagForwardOnly)

But the following WMI query against the native Citrix provider does return data:

Set objWMIService = GetObject("winmgmts:\" & strComputer & "\root\Citrix")
Set colItems = objWMIService.ExecQuery("SELECT * FROM MetaFrame_Session", "WQL", wbemFlagReturnImmediately + wbemFlagForwardOnly)

Also the counter data can be seen in Administrative Tools | Performance

- Add a counter
- Select the ICA Session performance object
- Select the All instances radio button
- Click Add

The following may help to resolve the issue:

- Start the WMI Performance Adapter service
- Start the Citrix WMI service
- Run the command winmgmt /clearadap
- Run the command winmgmt /resyncperf
- Restart the Windows Management Instrumentation service

Otherwise re-register and recompile WMI providers.

Microsoft:

c:
cd %windir%\system32\wbem\
for %i in (*.dll) do RegSvr32 /s %i
for %i in (*.mof, *.mfl) do Mofcomp %i

Citrix:

c:
cd "C:\Program Files\Citrix\System32\Citrix\WMI"
for %i in (*.mof, *.mfl) do Mofcomp %i

Run the following commands:

winmgmt /clearadap
winmgmt /resyncperf

Restart the Windows Management Instrumentation service

If this does not resolve the issue reset WMI and repeat the above steps

c:
cd %windir%\system32\wbem\
net stop winmgmt
rmdir /s /q repository
rmdir /s /q Logs
mkdir Logs
net start winmgmt

How to troubleshoot WinMgmt-based performance counter errors
http://support.microsoft.com/kb/266416