Verify the following: 
  1. Confirm Blackbaud AppFx Configuration Manger is set to use network service. Under "Add application user"
  2. Confirm BBAppFx Connection String is correct in "[drive]:\Program Files\Blackbaud\bbappfx\vroot\web.config.
  3. Confirm that NT Authority\Anonymous Logon, NT Authority\Network Service, and bbportalwebuser have the appropriate roles applied in SQL Management Studio
  4. Confirm if ASP.NET Impersonation is enabled on the bbAppFx service under the Default Web Site within IIS
To verify ASP.NET Impersonation, perform the following:
  1. Open up IIS on the NetCommunity web server or server where NetCommunity is installed
  2. Expand Sites > Default Web Site > Click bbAppFx
  3. Click on Authentication under the IIS section
  4. If ASP.NET Impersonation is enabled, use bbportalwebuser for the credentials under configuration.aspx for the Blackbaud Core Components
If issue still persist the reason is because the database server is on a different domain from the web server. If this is the case complete the following troubleshooting steps.
  1. Access the SQL Server
  2. Create new Database User
  3. Grant Rights to BBNC Database
  5. Log out of SQL SERVER and Database server
  6. Log into Web server.
  7. Edit Web.Config file in following folder [drive]:\Program Files\Blackbaud\bbappfx\vroot
  8. Locate Connection String: <add name="BBInfinity" connectionString="Server=SERVERNAME;database=DATABASENAME;integrated security=sspi" />
  9. Remove "integrated security=sspi" and replace with"User ID=SQLuser;Password=SQLpassword;"
  10. Where "SQLuser" and "SQLpassword" is the user you set up in SQL Server