Invoice voucher number missed

Dear all,
i have some case. i'm doing invoice entry then when I want to do a match with the Receive my computer is hang. so i turn off my computer and then i do the invoice entry again with no issue.
in the end of day, i do check my data, apparently there are some voucher number are missed. to my knowledge, voucher number of invoice is a running number that is generated by system.
at what time the system generates the voucher number? is there any setup to control that invoice running number?


thanks n regards,


Suryadi