Duplication of Vouche numbers

i dont know how i can fix these proplem i needd the voucher number not dublicate what i can do to fix this proplem in axapta 3.0

Journal numbers, Duplication of Vouche numbers etc., In spite of escalation to Microsoft so many time by our Implementation partner, we could not get any solutio from Microsoft.
Voucher numbering being a statutory o

bligation to meet Auditors requirements, out of compulsion the partner provided Customized solution

has anyone faced similar problems?

why this is proplem happen?