Default [Q]can't go back to stock

Am on xperia m.I already raised question in our section didn't get any response
Am in cm11. I want to go back to I tried to flash my FW in flashtool it gave me error .

and in flashtool folder there was another file.In that file it was like this

Java IOexceptional: can't read from source(this is only starting first line)

Second question
Can I go back to stock in cwm ,I mean flashing custom kernel and from cwm flashing zip . I made flashable zip from ftf(extracted system and meta folder and zip using compression to store)

Anyone please help

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