I created the membership tables etc. with aspnet_regsql -S myServer -E -A mr -d anExistingDatabase. I can see these changes in SQL Server Management Studio, when I connect as myself through Windows Authentication.
I could not see these changes in SQL Server Management Studio, while logged in as a readwrite user. I cannot make the appropriate changes in Visual Studio 2008 [Project/ASP.NET Configuration] either. When I click on the Security link in ASP.NET Web Application Administration I get the following error:
"There is a problem with your selected data store. This can be caused by an invalid server name or credentials, or by insufficient permission. It can also be caused by the role manager feature not being enabled. Click the button below to be redirected to a page where you can choose a new data store."