Hi, it is very interesting. I am running OTHIRE, and have always been able to spill blood onto a gravestone and a lever.
Could you first confirm, what version of othire you are using? In particular, your containers. Please have a look here:
OpenTibia Server for Tibia 7.72. Contribute to Ezzz-dev/OTHire development by creating an account on GitHub.
github.com
Second, could you look at those objects in objectbuilder? For a normal "grave" (the one with the dirt and the headstone) and the white flat gravestone, you should be able to spill on them. In objectbuilder in properties, they should be "unmoveable". But the other 2 gravestones, the broken one, and the up arrow one, you are not able to spill on them, as they are set as "unmoveable" and "unpassable". Could you check to see about that as well?
The error you receive is very odd in that, when there are things I cannot spill on, the message is "you cannot use this object".
Hopefully this is a starting point until someone better can help out; please let us know of the above, and perhaps a good solution can be found.