Can't add website + Upfront Builder Problems


Its the first time I'm writing in support today and after researchs I couldn't find solution to my problems.

So, I've just bought and successfully installed WPMUDEV the first time, but the builder was buggy, I then decided to uninstall all the plugins(WPMUDEV + UPFRONT) and to re-install them.

But now, after two successful installation, I cant link my website to the dashboard even if I'm correctly logged in WPMUDEV : when I hit "Finish Setup" it says : "We could not find your new website.
Please make sure you have followed steps above."

And for Upfront Builder I have 2 bugs : I cant drag anything to the page and I cant create a new theme in the builder, instead of a new page it displays : "Not Found

The requested URL /create_new/essai was not found on this server."

I dont really know what to do and I'm looking for some help,
Thanks for your concern,