I actually haven't had the opportunity to test on LAN/MP quite yet. Sorry you're having this trouble. Have you tried with SynergiesHIGHLOOT above TOP - Diablo UI? Without it? Both of you are using the same exact version of mods?

Wouldn't mind hearing if others are having similar problems.

Heyo I am the feller who was playing with Vance on LAN. We had the same mod versions installed and we tried just about every combination of the three mods to get it to work. We tried playing with Overhaul at the top and Synergies below without the Highloot. We also tried creating a multiplayer match instead of a LAN, but every time one of us attempts to join the other the one who is hosting crashes and the person joining becomes host and loads in. We even went so far as to empty everything else before attempting to run the mod again, we deleted all our saves from past games, deleted all other mods and unsubscribed so they would not redownload, I mean just about everything was cleaned out of our Torchlight folders that had to do with any other mod. Like he said we really like what the mod accomplishes due to us both being huge fans of the Diablo series, but it seems his necromancer and my nethermancer are never meant to be played in the same game haha.

Jordan summed it up well your mod is boss and is a great idea! Let us know if you need anthing from us, would kill for mutiplayer on the mod.
Thanks

If you wouldn't mind, could you try testing these mods for me and tell me if they work with Synergies on LAN/MP? Or anyone that's reading this.

MOD #1[mega.co.nz] - This one has both Recnam Rising + Forbidden Vault removed.

MOD #2[mega.co.nz] - This one has just Forbidden Vault removed.

MOD #3[mega.co.nz] - This one has just Recnam Rising removed.

Try using just MOD #1 with Synergies right below it in the load order. You'll place the mod in this folder:
C:\Users\*USERNAME*\Documents\My Games\Runic Games\Torchlight 2\mods

NOTE: Only place one in the folder above. Don't download all and place in folder all together. It will make things easier and less confusing. If you see 2x "Torchlight Overhaul Project - Diablo UI" in the mod launcher, look at the version number. You'll want to use only the newer mod version.

If it doesn't work then the others probably wont work either. But if it does, could you try MOD #2 and #3 after? This will narrow down which mod is causing issues with Synergies. If none of them work, then I'll probably wait to fix the MP crash with my brother in the next couple of weeks.

I'll give credit for helping me narrow down the reason behind this mod not working on LAN/MP with Synergies.

I'm going to be away for the weekend so I probably wont be able to respond to anything till Sunday.

My fiance and I were having the same multiplayer issue (host crashes on player joining). At that time, all we were using was Cosmetic Slots, TOP-Diablo, and Synergies. We attempted to test the mod linked here in the discussion.

Using just MOD 1 and the latest Synergies update, the game crashed on loading to the main screen--the "Curses!" screen with the error report box popped up. The loading screen, in the brief moment that I could see it, appeared to be the default loading screen without the Diablo style embellishment.

My buddy and I downloaded Recnam's and Forbidden Vault separately and they both crashed the game out. Haven't tried your MOD 1 yet, will later

Thanks guys for testing. Really appreciate it. There probably wont be any updates until I get this resolved. I'll be testing where the issue lies with my brother here in the next couple days. Hopefully I can find the issue pretty quickly and start adding in a couple other mods I've been waiting to put in this pack.

Any idea what the other buggy mods might be? My buddy and I are working on testing

Ok as far as we've tested, all the add-on dungeons don't seem to work. Aegis Crypt and Greed's Lair also cause the crashing issue.

You tested Aegis/Greed's by themselves with Synergies? Hmm..I might have a few minutes to remove them from the mod real quick and upload it (not on the workshop) to see if it works. Like I said though, I wont be able to test for a couple more days so if you guys could keep supplying feedback that would be great!

Yes, we tested Aegis and Greed's by themselves with Synergies. And as far as we've tested everything else works. Just the added dungeon mods. Aegis, Greeds, Forbidden, and Recnam's cause crashing (fully tested just those and Synergies).

Thank you. I'll try to get a version without those included uploaded within the next hour or so. I'll post it here after. I gotta compare the files of those dungeons with all the other mods to make sure nothing was merged between them. If needed, remove the merged code and then the files/empty folders after.

We are trying to unpack your mod and remove said files ourselves, gonna try and see if this works for us

Good luck unpacking it :P
Maybe you'll have better luck than me. But when I tried, it always took forever and most of the time got an error forcing me to restart the unpack process. There's something in the Diablo UI that causes this as it did the same thing to me. If you read back in Diablo UI's comment section, someone else says they get the same issue. If you're persistent, eventually it will unpack. You'd probably be better off trying to unpack the UIMC version or Vanilla UI version.

EDIT: In the UIMC/Vanilla version you'd still have to remove Recnam/Forbidden Vault also.

Here's another mod to test with Aegis, Greeds, Forbidden and Recnam removed. Hopefully this will work.

https://mega.co.nz/#!n8pVzIbA!QOefUCExvqoIiWop-nc8CqUqqNAwfHUXeYC5pxZBVNM