Hello my name is Mikolaj.
I have problem with my Forge and Foundry vtt.
it seems so at i cant boot up my version 300 too the old version of foundry from v11 to v10
because when i doing everything like in this topic (below) my site dont starts up or its sending me on this site.
Pls help ;(
Hi @wisnia 
It sounds like your world might not be compatible with v11.
Which system are you using, and which version of Foundry are you using?
This article should help you to change your Foundry version on Forge 
Foundry VTT version selection
Remember, after setting the Foundry version, make sure to update your systems and modules. You can do this by navigating to The Bazaar and updating the packages from the “Updates Available” button, if there are any updates.
Also make sure to Stop and Start your server from The Forge
If this does not help you solve your problem, please post a screenshot of what you are running into! I’m sure that will help to add some context. Please also check in your dev tools console (F12) to see if there are any errors there, since modules which aren’t compatible can cause issues. I recommend testing with Safe Configuration which tries to load your world without any modules enabled.
Hope that helps!
v11.801
5e D&D
all of my modules are up of date
and before i chenge version i stop server re-updete modules and start server again on version v10
I’m sorry, v11.801 isn’t a valid Foundry version 
I’m not certain that I’m following what your issue is.
Could you please:
-
Post a screenshot of your dev tools console (F12) when you launch your game, to see if there are any errors when you start your game
-
Post a screenshot of your Foundry server logs when you try to launch your game to see if there are any errors. (You can click this button on The Forge setup screen)
fine,i do it right now
Thanks! Yeah, looks like incompatible modules.
Could you please try to disable all modules and see if it works?
Most modules do not support v11 yet.
If you need these modules, we will need to roll back your Foundry server version to v10.
Do you use Game Manager?
Yes im Story Teller subscriber
Thanks
Go here Game Manager setup and set the version to Forge Recommended (v10 Stable) as pictured here:
Then, Stop your world here
Then, on The Forge, scroll to the bottom and make sure your game is using the Default Game Manager version of Foundry
Then, go to the Bazaar and Update your modules to v10 versions.
Then, after the updates are done, try to launch your world again.
I did all by u instrucktions
That error usually means the system cannot launch.
Please go here and post a screenshot of the Bazaar front page which includes your configured Foundry version
Then, please go here to the dnd5e Bazaar package and post me a screenshot of what you see, like this:
Alright, nice
Thanks. Everything seems to be rolled back to v10 compatible versions.
Could you please also check the game’s configured version to make sure it’s set to use the Default Game Manager version as well?
This was on The Forge, scroll to the bottom and make sure your game is using the Default Game Manager version of Foundry.
Great!
Alright, last thing:
- Stop your server
- Launch in Safe Configuration
If this still does not work, you will likely need to restore the backup you took of the world from before you migrated to v11.
How should i do it,i do not remember so i make some backup of my world
See Backing Up Your Forge Content Restoring a World Backup section.
If you are using Game Manager, then Forge would likely have exported a backup of the world for you automatically if you did not export one when prompted to upgrade your world for v11. The exported zip is likely in your downloads folder.
See Backing Up Your Forge Content Restoring a World Backup section.
If you are using Game Manager, then Forge would likely have exported a backup of the world for you automatically if you did not export one when prompted to upgrade your world for v11. The exported zip is likely in your downloads folder.
If you do not have a backup from v10, then we can likely figure out where the issue is coming from by checking the Foundry server logs again. It should tell us why the server cannot start.
If you do not have a backup, and the world data had already been migrated to v11 and can’t run on v10 anymore, then you will need to update your Foundry version to v11 and disable the modules which don’t work yet.
It’s very important to check module compatibility before upgrading your Foundry version if you rely on modules heavily
It’s also very important to always make a backup of your world before upgrading.