Permission denied while accessing /proc/<pid>/exe - linux

Question

I am having trouble accessing the file in /proc filesystem
My process once started writes in a log file .My process was stopped and when i checked the logfile to see where it encountered the problem and found "permission denied".
it goes to the /proc directory ,fetches PID via getPID() and fires open() using O_RDONLY to read /proc/<pid>/exe
but after firing i get an error "Permission denied".
I did some research and found that kernel enforces some restrictions while accessing certain files in/proc ,but i have 20 process all accessing the same /proc/<pid>/exe ,but only one facing this problem ..
CHAR fn[100];
159 CHAR args[500];
160 CHAR ProgName[50];
161 CHAR *arr[6];
162 CHAR *buf;
163 CHAR ProcessId[10];
164 static int count_try = 0;
165
166
167 memset(fn,0,100);
168 memset(ProcessId,0,10);
169 sprintf (ProcessId,"%d",Pid);
170 strcpy(fn, "/proc/");
171 strcat(fn, ProcessId);
172 //strcat(fn, "/elf_prpsinfo");
173 strcat(fn, "/exe");
174
175 if ((psp = open(fn, O_RDONLY)) == -1)
176 {
177 perror("GetProgName:ps open::");
178 exit(ERROR);
179 }