Protect your post or your link by using [hidepost] and [/hidepost] between the protected content.
=The content still display after I put [hidepost] and [/hidepost] =
Double check your tag, it must be [hidepost] and [/hidepost], I tested it and it work perfectly. If you think its a bug, feel free to drop me a email or comment on plugin's page.
=Hard to Custom text...=
Goto Option -> Hidepost, and change Show Text to whatever you want. Note that %login% is the link to login page, and %register% is the link to register page. You should leave this unless you know what you are doing.
=Using the previous version?=
If your version less than 2.2 and you are using the [protect] tag, you must change all your tag to [hidepost] and upgrade to lastest version to have many new feature.
=The text "Please login or register not display" but the content still be hidden=
Go to Option page and uncheck "Hide the text".