How To: I cannot add documents to a list island because the document folder is not available

Time to check your permissions!

In order to add documents to a list island, the workgroup must be a reader of the folder in Portal Documents.

Solution:

If the folder is a ROOT FOLDER

Go to Portal Tools -> Manage Portal Documents -> Manage Folders
Click the dropdown for the folder you want to add the documents from, and click Edit.
In the Readers list, move the Workgroup from the Left to the Right (giving it permission)
Decide if you want that change to apply to JUST that folder, or all the sub folders and documents inside
Click OK.

Solution:

If the folder is a SUB FOLDER

Go to Portal Documents and navigate to the sub folder that needs the permission changed
Click the dropdown for the folder, and click Properties
Open the Security for Readers panel
In the Readers list, move the Workgroup from the Left to the Right (giving it permission)
Decide if you want that change to apply to JUST that folder, or all the sub folders and documents inside
Click OK.

(The screen cap above is for Portal Versions 7.2 and higher - but it works the same! - S)