The server principal "XYuser" is not able to access the database "Ydb" under the current security context

Question

SQL2005 on winserver 2003. I have a view in Xdb that accesses tables in 2 different databases (Xdb and Ydb) on the same server. I have mixed mode security. I have a SQL user (XYuser) that has read access to all tables and views on both databases, yet when I try to access the view using a C# windows application I get the following error:
The server principal "XYuser" is not able to access the database "Ydb" under the current security context
This same scenario works under SQL 2000. I looked through the postings and tried to set TRUSTWORTHY ON on both databases but that didn't help. I can access any other views or tables on the SQL 2005 server, just not the one that joins the tables cross databases. Any help is much appreciated... john

Answer 1

This appears to be a Login/Database Mapping issue.  I was having this problem, but was able to resolve it as follows:
Using the SQL Server management Studio:
In the Object explorer, under the SERVER security folder (not the database security folder), expand Logins. 
That is: ServerName -> Security -> Logins
NOT: ServerName -> Databases -> DatabaseName -> Security -> Users
Select the Login that is having the troubles.  Right click on the Login and select ‘Properties.’
The ‘User Mapping’ page should list all databases on the server with a check mark on the databases that the Login has been mapped to.  When I was getting the error, the database in question was not checked (even though the Login was assigned as a User on the database itself).  Map the Login by checking the box next to the database name.  Set the default schema.  Then select the roles for the Login in the Database role membership list box.  I selected db_datareader and public.  After clicking OK to save the changes, the problem was resolved.
In order to ‘Map’ the Login, the Login must not already be as User on the database, so you may have to go to the database security (ServerName -> Databases -> DatabaseName -> Security -> Users) and delete the Login from the list of database Users before mapping the Login to the database.