OK, I looked at this problem extensively today. Turns out the problem is caused by some changes made to DNN in 5.1.3 and 5.1.4. If you're on this version, then that's the reason.
I have uploaded a new version of the module today with the fix in it : download from here - http://www.ifinity.com.au/Products/Url_Master_DNN_SEO_Urls
However, the fixed version won't create the pages for your existing portals. For that, you need to run a script. I've attached the script below - just copy / paste this into your host-Sql page, then update the 'portalId' value at the top of the script for your target portal id. Check the 'execute as script' box and click on 'execute'. This will create the pages for you.
Begin transaction
declare @portalId int
select @portalID = !_update_me_to_portal_id_!
if @PortalId > -1
BEGIN
declare @moduleDefId int, @moduleControlId int, @controlSource nvarchar(255)
/* insert an admin / Page Urls page for the new portal */
Declare @AdminTabId int, @tabPath nvarchar(200), @tabOrder int
/* find the admin tab for the portal by working backwards from the site settings control */
SELECT @adminTabId = pt.TabId
, @tabPath = pt.TabPath
FROM {databaseOwner}{objectQualifier}Modules m
INNER JOIN {databaseOwner}{objectQualifier}MOduleDefinitions md
on m.ModuleDefId= md.ModuleDefId
INNER JOIN {databaseOwner}{objectQualifier}ModuleControls mc
on md.ModuleDefId = mc.ModuleDefId
INNER JOIN {databaseOwner}{objectQualifier}TabModules tm
on tm.ModuleId = m.ModuleId
INNER JOIN {databaseOwner}{objectQualifier}tabs t
on tm.TabId = t.TabId
INNER JOIN {databaseOwner}{objectQualifier}tabs pt
on t.ParentId = pt.TabId
WHERE (ControlSrc = 'DesktopModules/Admin/Portals/SiteSettings.ascx'
OR ControlSrc = 'Admin/Portal/SiteSettings.ascx') --either dnn5 (desktopModules) or dnn4 (admin/portal)
AND ControlKey is NULL
AND t.PortalId = @portalId
SELECT @tabOrder = coalesce(max(tabOrder), 0) + 1 --taborder is the last tab in the host tabs
FROM {databaseOwner}{objectQualifier}Tabs t
WHERE portalId = @portalId
AND t.ParentId = @adminTabId
-- update the tab path for the page urls page
SET @tabPath = @tabPath + '//PageUrls'
/* look for the table */
IF EXISTS (SELECT * FROM sysobjects WHERE id = OBJECT_ID(N'{databaseOwner}[ifty_TabModuleCreation]') AND type in (N'U'))
BEGIN
if exists (select * from {databaseOwner}[ifty_TabModuleCreation] where completed = 1)
Begin
/* insert a new record into the tabModuleCreation table, in preparation for the sp to be run*/
insert into {databaseOwner}[ifty_TabModuleCreation]
(PortalId ,ControlSource ,TabName ,IsVisible ,DisableLink ,ParentId ,TabIconFile ,Title
,Description,KeyWords,SkinSrc,ContainerSrc,TabPath ,StartDate,EndDate,RefreshInterval,PageHeadText
,IsSecure,TabOrder,IsAdmin ,PaneName ,CacheTime,Alignment,Color ,Border,ModuleIconFile,Visibility
,DisplayTitle,DisplayPrint,DisplaySyndicate,SetDesktopModuleAdmin,DeleteTabOnModuleRemove,TabId
,ModuleId,ModuleDefId,Completed)
select @PortalId ,ControlSource ,TabName ,IsVisible ,DisableLink ,@adminTabId ,TabIconFile ,Title
,Description,KeyWords,SkinSrc,ContainerSrc,@tabPath ,StartDate,EndDate,RefreshInterval,PageHeadText
,IsSecure,@tabOrder ,IsAdmin ,PaneName ,CacheTime,Alignment,Color ,Border,ModuleIconFile,Visibility
,DisplayTitle,DisplayPrint,DisplaySyndicate,SetDesktopModuleAdmin,DeleteTabOnModuleRemove,TabId
,ModuleId,ModuleDefId , 0
from {databaseOwner}[ifty_TabModuleCreation]
where PortalID = (select MIN(PortalId) from {databaseOwner}[ifty_TabModuleCreation])
and ControlSource = 'DesktopModules/iFinity.UrlMaster/PageList.ascx'
select @moduleDefId = mc.moduleDefId
, @moduleControlId = moduleControlId
From {databaseOwner}[ifty_TabModuleCreation] tmc
inner join {databaseOwner}{objectQualifier}ModuleControls mc
on mc.ModuleDefID = tmc.ModuleDefId
where PortalId = @portalId
and ControlSource = 'DesktopModules/iFinity.UrlMaster/PageList.ascx'
/* run the addTab and Tab Module routine to create the tab */
exec {databaseOwner}ifty_AddTabAndTabModule @moduleDefId, @moduleControlId
END
END
END
commit transaction