Here is the message:

Error while running event on_tick (ID 0)
LuaTile API call when LuaTile was invalid.
stack traceback:
GlobalWarming/control.lua:525: in function 'checkNeighbor'
GlobalWarming/control.lua:554: in function 'checkSand'
GlobalWarming/control.lua:353: in function 'findSand'
GlobalWarming/control.lua:226: in function 'desertification'
GlobalWarming/control.lua:649: in function <GlobalWarming/control.lua:647>

Have the same error with v0.7.7.
I have fixed the issue with replacing Line 525 in "control.lua" with:
if neigh2 and neigh2.valid and neigh2.collides_with("ground-tile") then