Most probably they do not have the required access permissions to create a Document for those Suppliers/Clients, Inventory Locations or Document Templates.
To set detailed permissions, the administrator of the account should navigate to the Menu > Settings > View Users and Permissions:
In the next screen, choose to Edit User Permissions of the user(s) in question.
Once in the permissions page of a specific user, click 'more' next to the 'Documents (Inventory Transactions & Invoices)' to display the detailed permissions for Suppliers/Clients, Inventory Locations and Document Templates 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: