Adriana,
With regards to your question, since you're using Community Edition of Rally, you only can have 1 Workspace and upto 5 projects therefore my question would be what exactly you meant by : "I was trying to create a new environment for another project" ?
If you're trying to create a new Workspace it will not be possible since most likely you've been already using one (Workspace) and as mentioned, that's maximum you can have in the Community Edition . And if you already have 5 projects in this very Workspace, you won't be able to create a new one per information mentioned above. I hope that helps.
Kind Regards,
Piotr