Callback from Webdynpro to Workflow

Good day,

I need to do a callback from a webdynpro application to the workflow that started the WebDynpro. This is the code I have so far-I

TRY.

CALL METHOD WDEVENT->GET_DATA

EXPORTING

NAME = 'SAPWFCBURL'

IMPORTING

VALUE = SAPWFCBURL

TRY.

CALL METHOD CL_SWF_IFS_WS_EXPORT=>LAUNCH_CALLBACK

EXPORTING

CALLBACK_URL = SAPWFCBURL

EXP_PARAMS_NVP = I_PARAMS.

CATCH CX_SWF_WS_HTTP_EXCEPTION .

CATCH CX_SWF_IFS_EXCEPTION .

ENDTRY.

I read in previous Sdn posts about how to fill this parameter - SAPWFCBURL. In WebDynpro , there is a parameter WDEVENT OF type CL_WD_CUSTOM_EVENT. It uses the method GET_DATA to read the parameters in the called URL. Hence I am doing the same.

However I am running into an exception - CX_SWF_WS_EXCEPTION.

Obviously I am missing something. Any advice is greatly appreciated.

Thanks, Liz