Please disregard this message

I think this is something really simple, but for the life of me can't see what I am doing wrong.

I have a table:

ID ForeignKeyID Date

I want to get the maximum date for each foreignKeyId.

When I do this:

SELECT ForeignKeyID, MAX(date)
FROM MyTable
GROUP BY ForeignKeyID

I get this error:

Each GROUP BY expression must contain at least one column that is not an outer reference.

Can someone explain this to a brain dead person, please?

Thanks