does any one here know the probable reason???

Yes, it's very simple. From time to time, especially towards the end of the month, MyLot does 'housekeeping' and they delete some discussions that violate the guidelines. Obviously, if you happen to have responded to those discussions, your responses are deleted too and you can't earn on those responses. The good news is that, when they delete stuff, the available money is redistributed, so you can often find that your earnings go up a few pence soon after they went down. It's all swings and roundabouts, really, and MyLot are VERY fair. I think it does say somewhere that your earnings aren't final till the end of the month, when they work out what profits to share. The best way to avoid having your earnings drop is to know the guidelines and make sure that you don't post anything yourself that violates them ... and also make sure that you don't respond to discussions that might be deleted. You can't be right all the time, of course, but you can avoid 'losing' so much to adjustment.

no dear it doesn't happen with me yet i think it can be due to service problem keep smiling