I just installed an old Episerver site on my laptop and got the error "The Trust Relationship Between The Primary Domain And The Trusted Domain Failed" continuously when trying to log in. It did not matter whether I inputted a correct username and password or just random gibberish, the error would always appear. What solved it for me was to go to web.config file and go to system.web. I changed the default membership provider from "MultiplexingMembershipProvider" to "SqlServerMembershipProvider".
From:
<system.Web>
<membership defaultProvider="MultiplexingMembershipProvider" userIsOnlineTimeWindow="10" hashAlgorithmType="HMACSHA512">
<providers>
<clear />
<add name="MultiplexingMembershipProvider" type="EPiServer.Security.MultiplexingMembershipProvider, EPiServer.Framework" provider1="SqlServerMembershipProvider" provider2="WindowsMembershipProvider" />
<add name="WindowsMembershipProvider" type="EPiServer.Security.WindowsMembershipProvider, EPiServer" deletePrefix="BUILTIN\" searchByEmail="true" />
<add name="SqlServerMembershipProvider" type="System.Web.Security.SqlMembershipProvider, System.Web, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" connectionStringName="EPiServerDB" requiresQuestionAndAnswer="false" applicationName="EPiServerSample" requiresUniqueEmail="true" passwordFormat="Hashed" maxInvalidPasswordAttempts="5" minRequiredPasswordLength="7" minRequiredNonalphanumericCharacters="0" passwordAttemptWindow="10" passwordStrengthRegularExpression="" />
</providers>
</membership>
To:
<system.Web>
<membership defaultProvider="SqlServerMembershipProvider" userIsOnlineTimeWindow="10" hashAlgorithmType="HMACSHA512">
<providers>
<clear />
<!--<add name="MultiplexingMembershipProvider" type="EPiServer.Security.MultiplexingMembershipProvider, EPiServer.Framework" provider1="SqlServerMembershipProvider" provider2="WindowsMembershipProvider" />-->
<add name="WindowsMembershipProvider" type="EPiServer.Security.WindowsMembershipProvider, EPiServer" deletePrefix="BUILTIN\" searchByEmail="true" />
<add name="SqlServerMembershipProvider" type="System.Web.Security.SqlMembershipProvider, System.Web, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" connectionStringName="EPiServerDB" requiresQuestionAndAnswer="false" applicationName="EPiServerSample" requiresUniqueEmail="true" passwordFormat="Hashed" maxInvalidPasswordAttempts="5" minRequiredPasswordLength="7" minRequiredNonalphanumericCharacters="0" passwordAttemptWindow="10" passwordStrengthRegularExpression="" />
</providers>
</membership>
Something about active directory maybe? Not sure.