Starting wflow template via a report

[Swami Bala]

Hello,
 
I am trying to trigger workflow template using standard fmodule like
SAP_WAPI_START_WORKFLOW & other fmodule like SWU_START_WORKFLOW. Though I
donot have any problem triggering wflow template using SWU_START_WORKFLOW, I
get an error message 'User cannot start task' when i tried to use the wapi
function module. I have passed all the mandatory parameters and I have all
authorization. I could not figure out the rationale behind the
wapi function module in erroring out. Is it the one should I use or there is
something I am missing here ?
 
Thanks
 
Swami Bala