You have to check on the database, not on the Server.  Open the database/Security/users/ tab and open advanced Settings of the dbo, check if sa is mapped to the Login Name.  I think the Login Name is missing.

After restore a database to an SQL Server the LOgin Names can not be mapped about all users have a different SID.

Login on SQL Management Studio and open a new Query page.  Then run following script after you changed with your database Name:

/*** Start Script ***/

use database

Go

exec sp_change_user_login 'Update_One', 'dbo', 'sa'

Go

/*** End Script ***/

If you have a other user Name on your Connection strings search also about that username on the database and then run same script as above after Change the dbo with the username of the database and the sa with the Login Name of the SQL Server security.

Sample:

/*** Start Script ***/

use database

Go

exec sp_change_user_login 'Update_One', 'dbuser', 'dbusername'

Go

/*** End Script ***/