I found the reason for the error. It is the keyword "Enums".

It should be "Enum". That is,

SELECT
    MoneyInOut.Date AS Date,
    MoneyInOut.InOut AS InOut,
    MoneyInOut.Currency AS Currency,
    MoneyInOut.Value AS Value,
    MoneyInOut.Comment AS Comment
FROM
    Document.MoneyInOut AS MoneyInOut
WHERE
    MoneyInOut.InOut = VALUE(Enum.MoneyInOut.In)

This single letter "s" caused so much trouble :)