good...
if you were laid off, there is nothing much you could have done.
In your RFE reply, if possible attach a letter from your previous employer stating that they laid you off. And, in your covering letter be sure to mention about the lay-off and that, you were forced to change employers.
I have read in this forum before that eventhough the RFE states "employment letter from the employer who filed the I-140", you can still provide an employment letter from your current employer. (Its just that the RFE text is of old format i.e pre AC21)
All that BCIS wants to know during adjucation is that, you're employed and you won't become a public charge.