Serious Connection Issues?

[BMSxRIO]

I can't figure out what the problem is but I'm fairly new to all this.

1-I've gone to my router and enabled UPnP
2-I've port forwarded 2100 for TCP/UDP (TCP and UDP Individually)
3-I've allowed exceptions for inbound and outbound rules for port 2100 via windows firewall
4-I've gone so far as to even turn off windows firewall completly.

I get 50 mbps on my computer so I know it's not like my connection is too slow.

Yet, whenever I try to host a game I get the message about how I need to make sure port 2100 can accept incoming connections.
Though I can still get my buddy to connect with Lobby I.P, shortly after connecting, we get the 2+2=5 desync error.

Has anyone found a solve for this? (Please try to keep it simple)

[BMSxRIO]

So below is a list of things I've tried to get my connection better. When I try to host a game after I click "host" it tells me to check my connection for port 2100. My friend can join through my IP over the internet, however we get a desync after just a few minutes and his side completely stops responding to me.

I've tried port forwarding TCP/UDP with port 2100
Turning off windows firewall
enabling in/outbound rules for firewall anyway
My UPnP is enabled.

I have no idea what else I can really do to help my connection. I have 50mpbs so I know it's not my or his connection specifically. What else can I do?

[vexed]

What router do you have?
I suggest you both rename/move your config directories and see if that helps with the desync stuff.
You both need to have the exact same versions of the game as well.

[NoQ]

Desync (2+2=5) is not a connection issue, it's a logic bug; +1 regarding cleaning user game data on both machines.