Error: element is not expected

I need to calculate NDVI and NDWI so I’m processing atmospheric correction on 2016 images.

Sometimes when the process is around 20% (for example) the programme says that the element expected should be (SENSOR_QUALITY_FLAG) and then the process is 100% terminated succesfully. Is it really ok?

While I’m writting this I’m processing another image and this process is at 99% since seven hours ago and I don´t know if that’s normal ¿should I cancel it?

Thanks

(sorry for my english)