Are you using projects? A user could have access to a view in a workbook directly from a link. And a user could also have access to see the project, but not see the workbooks in the project. What I would do is fix the rights on the project by pressing "Assign Permissions to Contents" and have all workbooks in the project inherit the same rights the project has. Warning, this is non-reversible.
What server version are you on? This screenshot is from version 9.0.
Thanks a bunch!! I tried to assign permissions to contents for the folder/project that I would like users to be able to access. Also, I assigned permissions at the workbook level. None of the above actions resulted in showing any workbook under those users, so the users still are unable to see any workbooks --- which is very strange. The version is 8.1.6. Pls advise. Thx a lot!!