reading wrong

hi all,
 My code works for the first time. When it repeat second time in the for loop, it have segmentation fault due to 0x002b96ac in fread () from /lib/libc.so.6 ( when i run debugger)
 Please explain what I did wrong. thanks a lot.

--------------------------
 // read in trunk and send trunk of each file until done fo each file and move on
       int result;
       if( size >= 2048)
       {
             for( int i= 0; i < count;i++)
             {
                  buffer= (char*)malloc(sizeof(char) *2048);
                  memset(buffer,'\0',2048);
                  result= fread (buffer,1,2048,fp);
                 
                  if (result != 2048)
                  {
                        printf(" Reading error in block 2048\n",stderr);
                        exit(1);
                  }
                  send(sock, buffer, 2048,0);
                  free(buffer);
                  fp= fp + 2048; //move fp to next block
                  printf("i is %d. next block \n",i);
             }
             
             //send the remainder trunk
             buffer= (char*)malloc(sizeof(char) *remainder);
           memset(buffer,'\0',remainder);
             result= fread (buffer,1,remainder,fp);
             if (result != remainder)
             {
                   printf(" Reading error in remainder ",stderr);
                   exit(1);
             }
             send(sock, buffer, remainder, 0);
             free(buffer);
       }