Firstly, as this uses the ADM module, you would need to ensure that the Dimensions licence is correct and includes the ADM module.
If the licence is incorrect then a new licence will need to be gained and applied for all users.
If hosted, ensure all users are logged out and only the hosting.admin account is being used and logged in in order to update the licence.
Confirming that the licence is correct, the below options would need to be reviewed to allow for the barcode printing functionality.
System Control Options:
On the System tab, click Options, System Control Options
Within the Records tab, ensure that the option for 'Store Documents in the Document Management System' is enabled. If it isn't, tick the option and then save.
User Records setup:
To enable the printing of barcodes for users please follow the steps below:
1. On the System tab, click User Records.
2. Navigate to the relevant user record and click on Edit.
3. At the bottom of the window, tick the option 'Print a barcode for Purchase Invoices and Credit Notes'.
4. Save and then have the user log off and back into Dimensions for changes to take effect.