If you get the above error in ASP.NET application, the user under which IIS is running does not have the permission to either select,execute,insert or update a table. The funny thing is, it does not provide the user name which is denied the permission (probably for security reason?) but it does say the dbo name.
Usually the user in this case is [NT Authority/Network Service]. You may want to grant DML permissions to [NT Authority/Network Service] so that it can select, update, insert and execute stored procedure.
The following command might fix your problem
GRANT SELECT, EXECUTE, UPDATE, INSERT ON SCHEMA :: dbo TO
[NT AUTHORITYNETWORK SERVICE]