Ensure the user is set up as an administrator with permission to create and edit nominal accounts.
This is commonly caused by the Chart of Accounts not being fully built. If your accounts have two layers, both layers need at least one entry each before the chart can be built. Look for grey warning triangles on incomplete entries and remove them before building.
If the Build option is still disabled or greyed out, contact the support team to investigate. If you have trouble reaching us, see Get support in Access Financials.