Because most probably they do not have the required permissions to create a Document for those suppliers/clients or Inventory Locations.
- To set detailed permissions, the administrator of the account should go to the admin panel > Users > Display All and choose to Edit the Permissions of the user(s) in question.
- Once in the permissions page, click 'more' next to the 'Documents (Inventory Transactions & Invoices)' to display the detailed permissions for Suppliers/Clients and Inventory Locations and set them accordingly. Repeat the procedure of setting the detailed user permissions for the rest of the pages by clicking 'more' at the tab of those pages. You can see an example of this below.
Or login to your account.