How would I grant select on a table being used in a different database to a user role in SQL?
Open SQL Server Management studio 2008.
Expand the server instance > Security > Logins > and locate the
log in you have having an issue with. 
Right click the user and select Properties.
Select User Mappings.
Locate the database you want the user to have access to and check
the checkbox in the map column. 
Set the correct database membership for this user and click OK.
Try your code again, be sure to qualify the path properly like
[database_name]..[Table_Name] in your FROM.