Pasted the error that caused a crash. Hope this is an easy fix or if anyone knows where there might be a conflict.

Error while running event beltSorter::on_gui_click (ID 1)
Value must be a dictionary in property tree at ROOT.count
stack traceback:
beltSorter/control/belt-sorter-gui.lua:229: in function 'storeConfigToCombinator'
beltSorter/control/belt-sorter-gui.lua:200: in function 'rebuildFilterFromGui'
beltSorter/control/belt-sorter-gui.lua:179: in function 'setSlotFilter'
beltSorter/control/belt-sorter-gui.lua:68: in function 'click'
beltSorter/libs/control/gui.lua:67: in function <beltSorter/libs/control/gui.lua:59>
(...tail calls...)
stack traceback:
[C]: in function 'newindex'
__beltSorter/control/belt-sorter-gui.lua:229: in function 'storeConfigToCombinator'
beltSorter/control/belt-sorter-gui.lua:200: in function 'rebuildFilterFromGui'
beltSorter/control/belt-sorter-gui.lua:179: in function 'setSlotFilter'
beltSorter/control/belt-sorter-gui.lua:68: in function 'click'
beltSorter/libs/control/gui.lua:67: in function <beltSorter/libs/control/gui.lua:59>
(...tail calls...)

What were you doing when the crash occurred and what version of the mod do you have? The current version is a rough update with some known issues to get v1.1+ compatibility. If I remember correctly, the workaround to the published version is to not try to blueprint or copy and paste units with configurations. "New" units (units without the filter configurations) should be fine.

It still isn't 100%, but if you want to give fixing it yourself a shot, here is an excerpt of a post I made in the v1.1 upgrade thread on how I further fixed my personal copy of the mod. I personally haven't gone back to see what else I could figure out yet, but the error codes seem somewhat similar to what I was running into.

So far I've been able to get it to stop throwing an error so you can blueprint or copy a sorter with an active configuration, but it doesn't actually paste the configuration settings into the new entity. To do that I ended up remarking out almost the entire beltSorterGui.storeConfigToCombinator function (lines 207-229 specifically) in belt-sorter-gui.lua. I'm still looking, but as far as I could tell it didn't actually do anything anyway...created some local variables, did some things to one of them and sent the results back to the other. Everything except the ability to blueprint and/or paste an entity with settings seems to be working without it. (Pasting settings with the Copy/Paste in the sorter's gui works.)

I had the same problem as Seeyeay.
I had just installed the Belt Sorder and when I wanted to configure the exit of the belts, I got the error message.
I am under version 1.0, with the latest Mod update

I am under version 1.0, with the latest Mod update

If you're only on v1.0 of Factorio, you might want to try manually (re)installing v0.7.1 (if you're on v0.8.0) or v0.7.0 (I read some reports of issues with v0.7.1 in another thread.) I'm on Factorio v1.1.6 myself and I've changed some other stuff in my personal copy of the mod (based on v0.8.0) so it's hard to tell, but I don't recall any difference that should affect backwards compatibility with Factorio v1.0. It is possible however there IS a difference and v0.8.0 doesn't work with Factorio v1.0 and/or when the dev made the update for the science packs in v0.7.1 they inadvertently made it using the 0.8.0 code for Factorio v1.1. (They'll say v0.18 of Factorio on the download page, but they'll work with v1.0.)