3089637 - My Inbox error: RFC call was not successful because of communication failure

Opening My Inbox has error. The error messages in browser console are:

RFC call was not successful because of communication failure 'The function call of /IWWRK/WF_TGW_TASK_DEFINITION failed; a field may have been assigned to the parameter ES_TASK_DEFINITION whose type is not compatible with this parameter'

RFC call was not successful because of communication failure 'The function call of /IWWRK/WF_TGW_QUEERY_TASKS failed; a field may have been assigned to the parameter ET_TASKS whose type is not compatible with this parameter'

SAP NetWeaver 750 or lower versions

IW_PGW 100 SP08 or lower SP levels

An exception was raised, TASKPROCESSING, IWPGW, /IWBEP/CX_MGW_BOP_RFC_COMM, /IWBEP/CX_MGW_TECH_EXCEPTION , KBA , CA-INB-FIO , Fiori UI for My Inbox Application , Problem