The securities commissioner may by order deny or revoke any exemption specified in item (8) or (10) of Section 35-1-310 or in Section 35-1-320 with respect to a specific security or transaction. No such order may be entered without appropriate prior notice to all interested parties, opportunity for hearing and written findings of fact and conclusions of law, except that the securities commissioner may by order summarily deny or revoke any of the specified exemptions pending final determination of any proceeding under this section. Upon the entry of a summary order, the securities commissioner shall promptly notify all interested parties that it has been entered and of the reasons therefor and that within fifteen days of the receipt of a written request the matter will be set down for hearing. If no hearing is requested and none is ordered by the securities commissioner, the order will remain in effect until it is modified or vacated by the securities commissioner. If a hearing is requested or ordered, the securities commissioner, after notice of an opportunity for hearing to all interested persons, may modify or vacate the order or extend it until final determination. No order under this section may operate retroactively. No person may be considered to have violated Section 35-1-50 or Section 35-1-810 by reason of any offer or sale effected after the entry of an order under this section if he sustains the burden of proof that he did not know, and in the exercise of reasonable care could not have known, of the order.