Unable to add new task via API - Input Parameter Missing

Unable to add new task via API - Input Parameter Missing

I'm following the spec at  http://www.zoho.com/projects/developers/tasklists-api.html#7 to Add a new task to a Project Task list - I think I have all of the required form items populated based on the provided sample,but I'm getting an error:

{"code":6831,"message":"Input Parameter missing"}

https://projectsapi.zoho.com/portal/{PortalName}/api/private/xml/task/add?apikey={ApiKey}&ticket={Ticket}

projId=f8044dc4a76d2d98e298090ee4ab5d05b3711e3d6848763c, 
personresponsible=aee2293d0f655f48, 
listId=f8044dc4a76d2d986e2974ab7fd72a8b6755b1c1035e80e0, 
todotask=Create me, 
taskdate=08-21-2012, 
pcomplete=0, 
duration=1, 
priority=None


I noticed that the documentation is inconsistent between the  Parameters to be passed and the   Sample Call

listid vs listId
percentcomplete vs pcomplete
personresponsible is show in the Sample Call but not in the Parameters to be passed.

I tried different combinations but still can't successfully create a task :-(

Could you please confirm the exact parameters required to create a task.

Thanks.