The method do_register return a Page Not Found error. On Concrete5_Library_Controller, line 128, a print_r on $this return that (is it right?):

Controller Object
(
[theme] =>
[sets:Concrete5_Library_Controller:private] => Array
(
)

[helperObjects:protected] => Array
(
[html] => HtmlHelper Object
(
[legacyJavascript:protected] => Array
(
[ccm.dialog.js] => ccm.app.js
[jquery.metadata.js] => ccm.app.js
[ccm.themes.js] => ccm.app.js
[ccm.filemanager.js] => ccm.app.js
[jquery.colorpicker.js] => ccm.app.js
[jquery.liveupdate.js] => ccm.app.js
[ccm.ui.js] => ccm.app.js
[ccm.search.js] => ccm.app.js
)

[legacyCSS:protected] => Array
(
[ccm.dialog.css] => ccm.app.css
[ccm.ui.css] => ccm.app.css
[ccm.forms.css] => ccm.app.css
[ccm.menus.css] => ccm.app.css
[ccm.search.css] => ccm.app.css
[ccm.filemanager.css] => ccm.app.css
[ccm.calendar.css] => ccm.app.css
)

)

)

[c:protected] => Page Object
(
[blocksAliasedFromMasterCollection:protected] =>
[cID] => 111
[attributes:protected] => Array
(
)

[error] =>
[pkgID] => 0
[cPointerID] => 0
[cPointerExternalLink] =>
[cIsActive] => 1
[cIsSystemPage] => 1
[cPointerExternalLinkNewWindow] => 0
[cFilename] => /register.php
[cDateAdded] => 2014-01-13 14:29:28
[cDisplayOrder] => 0
[cDateModified] => 2014-06-28 13:04:40
[cInheritPermissionsFromCID] => 111
[cInheritPermissionsFrom] => OVERRIDE
[cOverrideTemplatePermissions] => 1
[cCheckedOutUID] =>
[cIsTemplate] => 0
[uID] => 1
[cPath] => /register
[cParentID] => 0
[cChildren] => 0
[cCacheFullPageContent] => -1
[cCacheFullPageContentOverrideLifetime] => 0
[cCacheFullPageContentLifetimeCustom] => 0
[isMasterCollection] => 0
[vObj] => CollectionVersion Object
(
[cvIsApproved] => 1
[cID] => 111
[attributes:protected] => Array
(
)

[layoutStyles] => Array
(
)

[error] =>
[cvID] => 5
[cvIsNew] => 0
[cvHandle] => register
[cvName] => Register
[cvDescription] =>
[cvDateCreated] => 2014-04-06 20:15:31
[cvDatePublic] => 2014-01-13 14:29:00
[cvAuthorUID] => 1
[cvApproverUID] => 1
[cvComments] => Version 5
[ptID] => 5
[ctID] => 0
[ctHandle] =>
[ctName] =>
[isMostRecent] => 1
)

)

[task:protected] =>
[parameters:protected] =>
[supportsPageCache:protected] =>
[restrictedMethods:protected] => Array
(
)

[helpers] => Array
(
[0] => html
)

)

I have similar issues with some packages developed by me. I fix it with a workaround, but on a system page, I do not want to change anything. If someone know what's happening, please, share! :)

Thank you!