If you cant able to select sale or add while generating invoices in BUSY Accounitng Software,If you are login as sub user,it might be its your user restrictions,
you can check these things:
Step 1:First,login your company in BUSY as admin user.
Step 2:Go to Administration menu,
Step 3:click users,
Step 4:Open that Sub user in modify mode,
Step 5:Go to Menu Rights options,
Step 6:Click transactions,then check the check box in sales and then add or view, then save this configuration.
Step 7:After that re login to your company as sub user, then check you will able to add sales vouchers.