The mod Subsurface - build beneath your base! (1.1.10) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event Subsurface::on_tick (ID 0)
Error when running interface function aai-programmable-vehicles.set_unit_command: Error when running interface function subsurface.on_unit_change_mode: core/lualib/math2d.lua:33: attempt to index local 'pos' (a nil value)
stack traceback:
core/lualib/math2d.lua:33: in function 'ensure_xy'
core/lualib/math2d.lua:44: in function 'distance_squared'
core/lualib/math2d.lua:52: in function 'distance'
Subsurface/scripts/aai-miners.lua:60: in function <Subsurface/scripts/aai-miners.lua:45>
(...tail calls...)
stack traceback:
[C]: in function 'call'
aai-programmable-vehicles/control.lua:120: in function 'raise_event'
aai-programmable-vehicles/control.lua:1395: in function 'unit_set_mode'
aai-programmable-vehicles/control.lua:2683: in function <aai-programmable-vehicles/control.lua:2483>
stack traceback:
[C]: in function 'call'
Subsurface/scripts/aai-miners.lua:95: in function 'handle_miners'
Subsurface/control.lua:461: in function <Subsurface/control.lua:361>

What did you do? A vehicle following a path?

I had 9 haulers, 9 miners and two wardens following a path underground. something else went wrong in my game an only one stone patch spawned so the miners have been getting me stone. something with the path eh. might be all the haulers one the path or the miner im putting on it is also a destination let me remove it from the path and see if it fixes it.

I think that was it adding a mine that was a destination on the path. since it was underground it flagged as you mod. my apologies.

Can you send a screenshot of the path? Problem may caused by the "follow" action instead of just a fixed waypoint

It was the miner being added to a path that itself was a stop on. I've deleted that path.