Does this mean that people with 1.8 will not be able to join the server once it's 1.9? Or will the server still be compatible with 1.8.9?
Unfortunately, we cannot fix your game client. Try deleting and reinstalling it, make sure you try the vanilla 1.9 client, and make sure you are using an up-to-date version of Java.
I heard rumours about 2 months ago that after 1.9 Factions would be getting reset? When the 1.9 issues are fixed will factions be reset or is that false? Because if it were I would come back to the server.
Well, I don't know what to tell you then, the issue is definitely on your end, I can connect with 1.9 fine, as can most players.
Delete .minecraft/libraries. Run Minecraft in 1.9, shut it down. Restart it. Give me any errors you encounter.
Try thinking for a moment. When the server is fully in 1.9, all the new blocks and mobs will be added in. If you try to connect with a 1.8 client, all these blocks and mobs won't be recognised by your client, so you wouldn't be able to play. Don't you remember everyone complaining about having to get a 1.8 modified client even though the 1.7 clients were so op?
if the way Logo said did not work please try uninstall minecraft. empty recycle bin, go search "%appdata%" click on "Roaming" then delete the .minecraft file. this after that. this will officially remove minecraft from your computer. Now to download it again go to https://minecraft.net/download thanks. Reply if it worked or not.
If your game is crashing don't reinstall your game... Just go to your Video Settings and turn VBO and Vsync to ON and then your problem will be all fixed with joining with 1.9
I actually do know because it works for everyone else who has complained about this on MinecraftForums and any other huge minecraft website that I have looked at and said the same.