Valgrind errors even though all heap blocks were freed

I have recently developed a habit of running all of my programs through valgrind to check for memory leaks, but most of its results have been a bit cryptic for me.

For my latest run, valgrind -v gave me:

All heap blocks were freed -- no leaks are possible

That means my program's covered for memory leaks, right?

So what does this error mean? Is my program not reading certain memory blocks correctly?

ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 14 from 9)

1 errors in context 1 of 1:
Invalid read of size 4
   at 0x804885B: findPos (in /home/a.out)
   by 0xADD918: start_thread (pthread_create.c:301)
   by 0xA26CCD: clone (clone.S:133)
 Address 0x4a27108 is 0 bytes after a block of size 40 alloc'd
   at 0x4005BDC: malloc (vg_replace_malloc.c:195)
   by 0x804892F: readInput (in /home/a.out)
   by 0xADD918: start_thread (pthread_create.c:301)
   by 0xA26CCD: clone (clone.S:133)

used_suppression:     14 dl-hack3-cond-1

Also, what are the so-called "suppressed" errors here?

Solution

Yes, you are greatly covered, don't think that valgrind easily can miss a leak in user code
your error means that you probably have a +1 error in indexing an array variable. the lines that valgrind tell you should be accurate, so you should easily find that, provided you compile all your code with -g
suppressed errors are usually from system libraries, which sometimes have small leaks or undectable things like the state variables of threads. your manual page should list the suppression file that is used by default