Rockhorn Summit / Hot, Hot, Hot Quest

[Sfubi]

This lava rock is not accessible for collecting lava rocks but the one at rendtail's entrance is usable for the hot, hot, hot quest. Why?

http://i1282.photobucket.com/albums/a528/zabe1965/Screenshot_2014-04-26-13-05-17_zps9wupwj5w.png

[Madnex]

Because in that instance, someone else has already collected that one.

[Bigboyblue]

I have had this happen to me as well. Running solo. No one has got to it before me. For some reason I can't collect it.