The ID column on that table is an autoidentity integer column. The only way you could get this error is if the table does not have the autoidentity property enabled. So the table is not in the expected state.
The most likely way this happened is that you tried to copy your database by importing all the objects. Probably you are trying to upgrade a copy of your site to be safe in case something goes wrong, which is a good idea, but you cannot copy your database like that.
Importing objects from one database to another is not the way to do it, doing that all tables will lose all their primary keys, foreign keys, autoidentity and defaults.
To do it correctly you must make a backup of the database and then restore the backup to a new database. Or use a tool that can script off all the objects and data, like the Red Gate tools or this tool on codeplex.
Hope that helps,
Joe