Python Toolbox to Geoprocessing Service failed

Hi All:

I am new to ArcGIS any help is appreciate. :-)

I used ArcMap 10.1 to create Python Toolbox without any parameter. It ran successfully on desktop. I then published and ran successfully on Desktop using "GIS Server" and from the Web browser via REST service. I then add one parameter with type "GPString". Ran successfully on desktop but fail on desktop if using "GIS Server". It also failed on REST Service. Fail message is "Error executing tool: ERROR 000816: The tool is not valid".
I then copy the sample "Calculate Sinousity" from the help page ran successfully on the Desktop but failed the same way.



Thanks,
Thanh