just updated and now the mod always throws an error upon starting the game so I have to deactivate it... Following the debugging details:

beltlayer/data-updates.lua:2: beltlayer/prototypes/bpproxies.lua:137: attempt to index local 'structure_patch' (a nil value)
stack traceback:
beltlayer/prototypes/bpproxies.lua:137: in function 'make_splitter_proxy_sprites'
beltlayer/prototypes/bpproxies.lua:154: in function 'make_splitter_proxy'
beltlayer/prototypes/bpproxies.lua:162: in main chunk
[C]: in function 'require'
beltlayer/data-updates.lua:2: in main chunk
stack traceback:
[C]: in function 'require'
beltlayer/data-updates.lua:2: in main chunk

also, following a list of mods I have activated, in case of incompatibilities(everthing up to date atm and worked before I updated Beltlayer)...
AAI Industry 0.4.14
Advanced assembly machines 0.1.3
Alien Biomes 0.5.5
Alien Biomes High-Res Terrain 0.5.1
Beautiful Bridge Railway 0.18.1
Belt Buffer 0.18.5
BigStorageTank 0.0.8
Bottleneck 0.11.4
Bulk Rail Loader 1.0.4
Deep Mine 0.5.4
Even Distribution 0.3.18
Event listener 0.9.3
Factorio Plus Plus 0.18.8
Factorissimo2 2.4.2
Fast Long inserters 1.3.1
Gore 0.18.7
Informatron 0.1.8
Jetpack 0.1.19
KS Power 0.4.0
Lagerhaus Mod 0.3.0
Miniloader 1.11.1
Mining and Crafting Speed Research 6.0.0
Mining Drones 0.3.23
Personal Teleporter 0.3.11
PLutonium Energy 1.1.11
Portals 0.5.1
Powered floor 0.3.8
Ressource Spawner Overhaul 6.0.10
Robosubstation 0.2.0
Robot Attrition 0.4.2
RPG Items 0.18.9
RPG System 0.18.49
Skandragon's Advanced Solar 1.2.4
Treeees 1.0.1
Ultimate Belts 0.18.2
VortiK's Deep core mining 2.0.3
Warerfill 0.18.0

same here

I get the same on launch

I'm receiving the same error.

it looks like that structure_patch is a new optional property included with .18. The error, according to the factorio common error faq, indicates this property is being called with a 0 (null) value but it cannot be, it should always have some value. I guess? I'm not a lua modder, but I spend my free(non-factorio) time debugging other code. Anyway, I don't know the exact syntax/structure to fix this property and leave it included but I was able to adjust my own bpproxies.lua which let me start my game with BeltLayer enabled. The belts I had placed already are still working, so this should be a decent temp work around until the actual issue is resolved. On to my "fix".

In bpproxies.lua (i use Notepad ++) i did a find all in current document, searching for structure_patch. That returned 3 hits. I removed the reference from the "local function" (line 126) and "proxy_proto.sprites" (line 154) and then commented out (added -- at the start) to line 137 "deepcopy (structure_patch)..."

Saved that and replaced it in the zip file then relaunched factorio with BeltLayer enabled. Game loaded normally. Hope that helps.

This should be fixed in 0.6.1.

Seems ok now at least for me. Thanks a ton, great mod!