After updating to 1.9 I get this error when I try to load save.
Error while running on_configuration_changed: fws/control.lua:215: attempt to perform arithmetic on field '?' (a nil value).
Is it possible to fix?
(If not would perhaps disabling the mod loading saving then enabling the mod loading and saving again fix the problem or would that cause the mod to not properly work?)

edit: Actually I tested this and the same error appears even when I just try to start new game.

What other mods are you using, if any?

a lot.
I can give you a list if that helps but it will be long
here is the list of all files in factorio mod folder.
aai-industry-sp0_0.0.4.zip
aai-industry_0.2.4.zip
aai-programmable-structures_0.4.4.zip
aai-programmable-vehicles_0.4.8.zip
aai-signals_0.3.3.zip
aai-vehicles-chaingunner_0.3.1.zip
aai-vehicles-flame-tank_0.2.1.zip
aai-vehicles-flame-tumbler_0.3.1.zip
aai-vehicles-hauler_0.3.1.zip
aai-vehicles-laser-tank_0.3.1.zip
aai-vehicles-miner_0.3.5.zip
aai-vehicles-warden_0.2.1.zip
aai-zones_0.3.4.zip
angelsaddons-oresilos_0.4.0.zip
angelsaddons-pressuretanks_0.3.0.zip
angelsaddons-warehouses_0.3.0.zip
angelsbioprocessing_0.5.9.zip
angelsindustries_0.1.0.zip
angelsinfiniteores_0.7.3.zip
angelspetrochem_0.7.12.zip
angelsrefining_0.9.14.zip
angelssmelting_0.4.6.zip
artillery-bombardment-remote_0.16.7.zip
Barbed-Wire-Light-016_0.16.2.zip
Big-Monsters_0.16.6.zip
Big_Brother_0.4.6.zip
Big_Brother_Bobs_plugin_0.1.7.zip
Bio_Industries_2.6.13.zip
bobassembly_0.16.1.zip
bobclasses_0.16.2.zip
bobelectronics_0.16.0.zip
bobenemies_0.16.0.zip
bobgreenhouse_0.16.0.zip
bobinserters_0.16.8.zip
boblibrary_0.16.6.zip
boblogistics_0.16.23.zip
bobmining_0.16.0.zip
bobmodules_0.16.0.zip
bobores_0.16.2.zip
bobplates_0.16.5.zip
bobpower_0.16.8.zip
bobrevamp_0.16.3.zip
bobtech_0.16.6.zip
bobvehicleequipment_0.16.2.zip
bobwarfare_0.16.7.zip
buffer-warehouse_0.2.0.zip
BulkierTrainsBob_0.1.0.zip
bullet-trails_0.3.1.zip
Clowns-AngelBob-Nuclear_1.0.1.zip
Clowns-Nuclear_1.2.0.zip
Clowns-Processing_1.2.8.zip
CoppermineBobModuleRebalancing_0.2.0.zip
DayNightExtender_1.1.13.zip
EnhancedFlashlight_0.1.2.zip
Enhanced_Map_Colors_1.4.6.zip
Epic-Artillery-Sounds_1.0.0.zip
extendedangels_0.1.6.zip
ForceFields2_2.1.4.zip
fws_0.1.9.zip
helmod_0.7.11.zip
Induction Charging_1.5.14.zip
Laser_Beam_Turrets_0.2.0.zip
LogisticTrainNetwork_1.9.3.zip
miniloader_1.6.5.zip
minime_0.0.6.zip
Natural_Evolution_Buildings_8.1.4.zip
Natural_Evolution_Enemies_9.0.9.zip
Natural_Evolution_Expansion_8.0.3.zip
Noxys_Multidirectional_Trains_0.0.7.zip
Noxys_Swimming_0.0.4.zip
Noxys_Waterfill_0.0.13.zip
omnilib_2.0.46.zip
omnimatter_2.0.26.zip
omnimatter_crystal_2.0.7.zip
omnimatter_permutation_0.1.6.zip
omnimatter_science_2.0.4.zip
omnimatter_wood_2.0.15.zip
Orbital Ion Cannon_1.6.3.zip
PavementDriveAssist_2.1.6.zip
PickerExtended_3.0.3.zip
pushbutton_0.16.0.zip
pycoalprocessing_1.0.10.zip
PyCoalTBaA_0.0.31.zip
pyfusionenergy_1.0.7.zip
pyhightech_1.0.9.zip
pyindustry_1.0.10.zip
railloader_0.5.5.zip
Rampant_0.16.34.zip
RealisticPower_1.0.9.zip
reverse-factory_5.1.5.zip
rso-mod_3.8.1.zip
Sandros-fixes_0.2.1.zip
SantasNixieTubeDisplay_0.1.7.zip
Soundpack-alerts-and-sirens_1.0.1.zip
Switch_Button_0.1.7.zip
textplates_0.3.3.zip
Turtle_Speed_0.2.3.zip
UsefulCombinators_0.4.4.zip
Xagros_TUONELA_TurretDelay_1.16.1.zip
xcompat_bobvehicleequipment_0.16.2.zip

After further testing I figured that the if I disable omniwood it works so that is probably causing it.

Probably fixed for 0.10.

Can you give any ETA?