Interfacing LDR with atmega32
try adding the header 

#define F_CPU 1000000UL // (or 8000000UL or 16000000UL depending upon what
                        //frequency you want your Atmega32 to run at)


before or after you include util/delay.h
Proteus requires your Atmega's frequency to be determined beforehand. 

Comment if it still doesn't work out!