error in task gateway service for work flow

Hiie All,

I'm facing issue with task gateway service, ie..,

I have configured task gateway service and activated the service /iwpgw/taskprocessing by following the below link.

http://help.sap.com/saphelp_gateway20sp05/helpdata/en/29/801ec804854ee58c805f50b80480cf/content.htm

but while executing the TaskCollection service , i'm facing the below error .

message xml:lang="en">RFC call was not successful because of system failure 'Function module "/IWWRK/WF_TGW_QUERY_TASKS" not found.'.</message>

First thing is why the IWPGW service is calling IWWRK component (/IWWRK/WF_TGW_QUERY_TASKS) ?

Second is I have configured system alias as trsuted RFC to ECC system .

Pl suggest ..,

Thanks ,

Lokeswar.