Hi @AnchalG2, please check before queue processor pick the work object whether assignment is corrupted already. or queue processor routing the case to WL?, if  yes and assignment is worklist type check the routing logic whether it is set to route to the current user if it is current user then it will fail try to give the operator id based on business logic.

@AnchalG2 The error you're seeing occurs because the Queue Processor is trying to resume a flow and assign a task using the operator ID "System", which doesn’t exist in your environment. Pega does not allow creation of an operator with the exact name "System", which causes this failure. To fix this, update your queue processor activity or the flow logic to run under a valid operator ID that exists in your system. One common solution is to set the pxRequestor.pxUserIdentifier to a valid existing operator (e.g., "BatchUser" or another service operator with appropriate access) before calling any assignment-related activities. You can also check if the Queue Processor is using the right access group and context to execute actions. Another option is to avoid using ticket-based resumption from a background thread and instead restructure the logic to continue the flow through standard assignment or flow actions under a proper user context