Row not found or changed & LINQ

This is a particularly well-known error (see here, here, and here), but this is the second time that I’ve had to do a search on this error so I thought that I’d post it here so that I can find it more quickly. Anyway, when this error occurs, make sure that the NULL types in the LINQ dbml file match your SQL schema NULL types. Mismatches between the two seem to be a common cause of this error.