If you can successfully add users then everything is likely setup correctly. Typically, you should get an error message on the login page (provided by SharePoint). If you don't get an error message after logging in it is typically caused by one of two issues.
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On some occasions when configuring FBA your IE browser can get confused during the configuration process. In most cases closing all IE browser windows, opening a new IE instance will correct your issue.
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SharePoint will redirect the user back to location defined in the SRC attribute of your query string. Make sure this page isn't pointing back to your login page. Removing the entire URL should correct this issue.
If this doesn't correct your issue please send a screen shot of the /_layouts/SPSolutions/Delegation/DelegationStatus.aspx page to softwaresupport@sharepointsolutions.com.