DBS has been slapped with a £40,000 fine by the PIA and ordered to pay £20,000 costs because of poor compliance procedures.
The network failed to adequately check the compliance of a member who gave bad advice in 1995. The member is no longer with the network.
The regulator says the network fully co-operated with its investigation into the matter.
The 1,800-member network says it has compensated all investors who suffered a loss.
DBS says it has strengthened its compliance team to over 100 from about 20 since 1995 and has tightened compliance procedure to avoid repetitions of the incident.