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"Use Edit Log for transactions/masters, and digital signature for invoices/reports with Release 2.1. Download NOW!"
https://help.tallysolutions.com/docs/ts9rel54/faq/7788_c.htm

Will Tally.Server 9 Release 4.51 work with old versions of Tally?

No.

Tally.Server 9 Release 4.51 is compatible with Tally.ERP 9 Series A from Release 4.5 onwards.