I have just implemented ECTS in my environment and have everything working except for external users being able to login through the external URL they are assigned to. No matter what external user I add I get the same error message. The server could not sign you in. Make sure your user name and password are correct, and then try again.

After login failed I went to the event viewer and found the error description:

Event Type: Information
Event Source: ASP.NET 2.0.50727.0
Event Category: Web Event
Event ID: 1315
Date: 6/5/2010
Time: 1:45:17 PM
User: N/A
Computer: ECTSServer
Description:
Event code: 4006
Event message: Membership credential verification failed.
Event time: 6/5/2010 1:45:17 PM
Event time (UTC): 6/5/2010 8:45:17 PM
Event ID: 3e938e24e4134813ad8e0171f6948d1c
Event sequence: 2
Event occurrence: 1
Event detail code: 0

Application information:
Application domain: /LM/W3SVC/1192987454/Root-3-129202442485658579
Trust level: WSS_Minimal
Application Virtual Path: /
Application Path: C:\Inetpub\wwwroot\wss\VirtualDirectories\collab.domain.com443\
Machine name: ECTSServer

Process information:
Process ID: 3532
Process name: w3wp.exe
Account name: domain\service account

Request information:
Request URL: https://collab.domain.com:443/_layouts/ExternalCollaboration/login.aspx?ReturnUrl=Membership credential verification failed.fsitesMembership credential verification failed.fdaletest2
Request path: /_layouts/ExternalCollaboration/login.aspx
User host address: External IP address
User:
Is authenticated: False
Authentication Type:
Thread account name: ECTSServer\IUSR_ECTSServer

Name to authenticate: externaluser@yahoo.com

Custom event details:

For more information, see Help and Support Center at http://go.microsoft.com/fwlink/events.asp.

I have installed ECTS in a Multi server environment. Consists of ECTS server, SQL Server, and Adam Server. Please help have been banging my head on the desk for days now!