Error in Web Site Administration Tool

[Shimon Sim]

I have following error when I try to "Manage access rules". I am using my
role provider and wanted to know if this could be caused by my code.
Thanks.
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An error was encountered. Please return to the previous page and try again.

The following message may help in diagnosing the problem: Specified argument
was out of the range of valid values. Parameter name: site at
System.Web.Configuration.WebConfigurationHost.InitForConfiguration(String&
locationSubPath, String& configPath, String& locationConfigPath,
IInternalConfigRoot configRoot, Object[] hostInitConfigurationParams) at
System.Configuration.Configuration..ctor(String locationSubPath, Type
typeConfigHost, Object[] hostInitConfigurationParams) at
System.Configuration.Internal.InternalConfigConfigurationFactory.System.Configuration.Internal.IInternalConfigConfigurationFactory.Create(Type
typeConfigHost, Object[] hostInitConfigurationParams) at
System.Web.Configuration.WebConfigurationHost.OpenConfiguration(WebLevel
webLevel, ConfigurationFileMap fileMap, VirtualPath path, String site,
String locationSubPath, String server, String userName, String password,
IntPtr tokenHandle) at
System.Web.Configuration.WebConfigurationManager.OpenWebConfigurationImpl(WebLevel
webLevel, ConfigurationFileMap fileMap, String path, String site, String
locationSubPath, String server, String userName, String password, IntPtr
userToken) at
System.Web.Configuration.WebConfigurationManager.OpenMappedWebConfiguration(WebConfigurationFileMap
fileMap, String path) at
System.Web.Administration.WebAdminPage.OpenWebConfiguration(String path,
String appPhysPath, Boolean getWebConfigForSubDir) at
System.Web.Administration.WebAdminPage.OpenWebConfiguration(String path,
Boolean getWebConfigForSubDir) at
ASP.security_permissions_managepermissions_aspx.BindGrid() at
ASP.security_permissions_managepermissions_aspx.Page_Load() at
System.Web.Util.CalliHelper.ArglessFunctionCaller(IntPtr fp, Object o) at
System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender,
EventArgs e) at System.Web.UI.Control.OnLoad(EventArgs e) at
System.Web.UI.Control.LoadRecursive() at
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint,
Boolean includeStagesAfterAsyncPoint)