Microsoft® SQL Server™ reserves certain keywords for its exclusive use. It is not legal to include the reserved keywords in a Transact-SQL statement in any location except that defined by SQL Server. No objects in the database should be given a name that matches a reserved keyword. If such a name exists, the object must always be referred to using delimited identifiers. Although this method does allow for objects whose names are reserved words, it is recommended that you do not name any database objects with a name that is the same as a reserved word.
In addition, the SQL-92 standard implemented by Microsoft® SQL Server™ defines a list of reserved keywords. Avoid using SQL-92 reserved keywords for object names and identifiers.
The Microsoft Upsizing Wizard will upsize some fields with reserved names, but many do not. Use SSW Upsizing PRO! to determine if you have these invalid field names.
The following reserved words will fail in the 2000 and 2002 Upsizing Wizard. Other reserved words will not fail, but it is recommended that you change them to avoid future issues.
More info – msdn.microsoft.com/library