You recently upgrade your DNN version, after upgrade you cannot login to your website and get "A critical error has occurred. An unexpected error has occurred".

The database upgraded successfully and you don't see any errors in the server logs.

Step by Step to Fix it :

In your web.config try changing

<members defaultProvider="AspNetMembershipProvider">
<providers>
 <clear />

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

to

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

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