Ian Grieve looks at Locked Payables Transaction: You cannot display this record while another user is editing it and delivers some SQL code to help.
Locked Payables Transaction: You cannot display this record while another user is editing it | azurecurve
Payables & ReceivablesInstall, Upgrade & AdminMicrosoft & the GP Ecosystem
Archived post from 2011. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.