Hi,
How long have you been using the tool does matter as this would be a primary condition to be met. Besides, the situation could be due to insufficinet privileges to the account used by ADAudit Plus where it may not have proper permission to write data to the archive location.
ADAudit Plus stores information on respective database tables e.g. AUDComputerAuditinfo, AUDLogoninfo etc. The archiving is set for each table (in this case 90 days).
Archiving happens when the below conditions are met.
1. The default database table of the associated report category is full when it crossed 500000 events
2. The last entry in the table is older that 'n' number of days where is the given value for archiving.
Hope it helps.
Regards,
ADAudit Plus Team