My only thoughts are:
1.) are you sure that the wood is hickory, not pine? (yellowish stuff, pine tar resins?)
2.) is the wood seasoned, not green?
3.) Your not using that Pinion wood they sell for chimineas are you?
I'm with Pat though, yellowish stuff looks kinda like grease......but it should be
soft enough just to scrape up with a spoon and not require chipping.