Check the Initial Catalog parameter in your connection string. It may be that your code is looking in the wrong database for the Projects object.
For example, if you have database syncing setup in such a way that only a subset of the master-database's tables are transferred, you can encounter this error if Linq to SQL is expecting all tables to be in the database pointed to by the connection string.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…