DaemonUmbra

Looks to me like you're missing a mod

Can you connect to the server locally with localhost as the IP?

Whatever your public IP is, assuming you've forwarded your ports

Can we focus on one issue at a time?

Go into your .minecraft folder and in your options.txt set fullscreen to false

Did you set an IP in your server.properties file? If so, blank it out and let the server automatically determine its IP

Do you know what changed between the two pack versions?

That's not a debug.log

Please read the Logs section of my signature below and provide the appropriate log in the appropriate manner.

Please read the Logs section of my signature below and provide the appropriate log in the appropriate manner.

How did you install Forge?

Please read the Logs section of my signature below and provide the appropriate log in the appropriate manner.

You did not read my signature

Please read the Logs section of my signature below and provide the appropriate log in the appropriate manner.

1.7.10 is no longer supported on this forum due to its age. Please update to a modern version of Minecraft to receive support.

Can I ask what changes to Forge you plan to propose?

1.7.10 is no longer supported on this forum due to its age. Please update to a modern version of Minecraft to receive support.

I believe this is now done by making sure you don't register any blocks/items/etc and setting any network connections you use to allow VANILLA or MISSING

1.7.10 is no longer supported on this forum due to its age. Please update to a modern version of Minecraft to receive support.

Please read the Logs section of my signature below and provide the appropriate log in the appropriate manner.

Please provide debug.log

You change the Java version per-installation/profile

1.8.9 is no longer supported on this forum due to its age. Please update to a modern version of Minecraft to receive support.

If it's still crashing provide a new log

Advanced Skin Customization is broken/poorly made and won't run on a server