Need Help Downgrading to a Previous MC Version

[igmdigm]

I'm trying to join my friends on a server that is on MC version 1.6.4 that is running Ultra Modded Survival. My launcher is running on 1.7. I've been trying as hard as I can to downgrade the MC version, but I am having enormous trouble doing so. I've tried replacing the launcher.jar as usual, which didn't work. I then looked in the Technic folder and removed the v1.7 .jar, but that failed to work as well. I'm assuming that it's either automatically updating MC or there are backups of the .jar which I am not aware of. I looked through the options to make sure I couldn't simply select the version I want, but could find none.

 

I've spent nearly an hour trying to fix this issue with no headway at all. Any suggestions would be appreciate, and my apologies if this is something that has been frequently asked before.

[Munaus]

your friend is running a pack from the platform? Then you shouldn't waste time hassling with downgrading and stuff like that, this is exactly what the platform was built for.

You download the pack and connect to the server, simple.

[igmdigm]

your friend is running a pack from the platform? Then you shouldn't waste time hassling with downgrading and stuff like that, this is exactly what the platform was built for.

You download the pack and connect to the server, simple.

I tried, but it didn't work like that. I probably should've elaborated a bit more.

This is the server in question.

And

This is the error I get when I attempt to join.

I suppose it might not necessarily be a problem with MC versions, but that's what I assumed it to be. Sorry I didn't post this initially.

Edited September 28, 2014 by igmdigm

[Munaus]

haven't seen that error line before. I'm unsure if this is a modpack or server issue...

 

Amaxter, creator of UMS, has posted a thread on this section for tech help with his pack. Might wanna ask there

I recommend posting the whole technic log (through a pastebin site) so he can analyze the issue properly

[igmdigm]

haven't seen that error line before. I'm unsure if this is a modpack or server issue...

 

Amaxter, creator of UMS, has posted a thread on this section for tech help with his pack. Might wanna ask there

I recommend posting the whole technic log (through a pastebin site) so he can analyze the issue properly

I see. Thank you for your time.

 

EDIT: I believe I may have found a way to resolve the issue. It's the fact that the modpack updated just yesterday.

Edited September 28, 2014 by igmdigm

[Kalbintion]

Bad packet IDs are very common with mods that have network information - if something is sent incorrectly (malformed) it can easily throw this error in regards to it as it may get an ID that is designed for a particular function (such as id 24 being related to mob information) that leads to nowhere, or to a function it wasnt expecting to get this information. These types of issues can be anywhere from mismatched versions between client<->server, to a badly coded mod, to an actual issue with FML. Without knowing what exactly updated, it may be impossible to know where the issue may lie. (tho it failing with a io.netty.codec.DecoderException is a new one to me)