Esp8266 IDE cant't find stdlib.h

Helo
I have instled 1.6.5
It is working ok for Arduino borards but when kompiling to esp boards tke kompitation end with an error "can't find stdlib.h".
I ued to have a nother problem, for some sketshes the kompilation just stopped in the middle of the process, and just stood there, with out any explination wath so ever. This was for some sketshes, e xamples in Arduino IDE all workef To corect this I reinstaled the esp ide, and after that the .h files is not fount. After that I reinstaled the hole Arduino enviremet, but with same result
I have surched the hard and found them, so I think it is a path matter.
I apolligise fot the languidge and spelling but Engish is not my native languidge
HansP