State the conditions that must be satisfied before an objection against the salaries tax assessment can be lodged and advise Brown whether a valid objection can be lodged in his case.
a. The objection must be lodged within 1 month from the date of the notice issued under s.51(3) of the Inland Revenue Ordinance.
b. The taxpayer must have reasonable grounds for objecting to the assessment.
c. The objection must be made in writing and must specify the grounds on which it is made.
d. The taxpayer must have paid or made arrangements to pay the amount of tax that is not in dispute.

In Brown's case, it seems that he may have a valid objection to the assessment, as he was advised by his tax consultant that the payment might not be taxable, and he acted on this advice. However, he should consult with a tax lawyer to ensure that all conditions for lodging an objection are met.