Any guesses as to why the "Add Value" button would be grayed out for a parameter so that you could not enter a parameter, but it is a required parameter so you have to have it to run the tool? (It is just a string).
Update: There appears to be a bug where it cannot handle entry of multivalue strings. If you turn off multivalue, you can enter a value, but then it does not work because it is supposed to be multivalue so it can populate a Python dictionary object.
At 10.0, one did not have to run the tool from the Desktop, only browse to it to create a geoprocessing service from it and it worked fine. Now one apparently has to run all of their server based tools from the Desktop just to be able to create a Geoprocessing Service from them as far as I can tell.