When upgrading from DNN 6.x to DNN 7.x, the installation wizard seems to miss an important setting in the web.config.  It also does not delete old DLLs from the /bin/ folder.  Because you are performing an upgrade rather than a clean installation, there are two versions of the AspNetMembershipProvider available, and the web.config may point to the wrong one.

Here is the fix.  Update your web.config to change the AspNetMembershipProvider section so that it uses the DotNetNuke.dll assembly instead of the DotNetNuke.Provider.AspNetProvider.dll assembly.

    <members defaultProvider="AspNetMembershipProvider">
      <providers>
        <clear />
        <add name="AspNetMembershipProvider"
          type="DotNetNuke.Security.Membership.AspNetMembershipProvider,
          DotNetNuke.Provider.AspNetProvider"
          providerPath="~\Providers\MembershipProviders\AspNetMembershipProvider\" />
      </providers>
    </members>

After removing “.Provider.AspNetProvider” from the configuration, everything should work fine.

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