Sorry, this site hasn't been shared with you

Hi,
I have a problem with FBA Authentication.
I installed everything correctly and I can add users and roles FBA.
I then added the user to a sharepoint group but when I try to login with Form Authentication to the site collection I get the message "Sorry, this site hasn't been shared with you"!!!!

Can anyone help me understand the problem?
Make sure that when you're logging in, you're logging in to a page on the site the user will have access to. For example if you sign out from a Site Settings page, the new user logging in may not have permissions to visit that page.

Otherwise though, it sounds like you are doing things correctly. Where are you assigning the user to the SharePoint group? If you'd like to do it from the FBA User Management page, make sure that 'Enable Roles' is unchecked on the FBA Site Configuration page.
I'll explain my situation.

The parameters 'Enable Roles' is unchecked on the FBA Site Configuration page and, when I add a new User, i see the SharePoint /Groups/Roles.

I have 1 Site Collection and One Sub-Site.
If I assign the FBA user to a group of Master Site Collection all work fine.
If I assign the FBA user to a group of Sub-Site (Subsite Owner) I can't access to sub-site pages and receive the message "Sorry, this site hasn't been shared with you".
This should work fine (and does in my environment). I don't think this will be related to FBA, and is more a permissions issue. Make sure that you're navigating to the home page of the sub site. It's possible that the pages contain content from the parent site (list web part, images from document library.....) and as such to view the site the user also needs permissions to the parent site. If you have a custom master page, then possibly it references items on the parent site.
thanks ccoulson.
The problem was that users of the subsite were not allowed access to the files of the theme :-)