Hi Khan,
SGEN decides the parallelism based on the objects to be generated. May be all work processes are occupied.
you will have to wait. Monitor the system (CPU and memory utilization). Check for swaps.
If the same situation continues, then you will have to kill the existing SGEN and start again.
Look at the option of program buffer resizing.
restart is recommended before you do so (just to clean up the buffers).