With the release of DotNetNuke 5.1, a lot of people are quickly updating their systems to the new version.
Url Master 1.13.x or earlier is not compatible with DNN 5.1. You should upgrade to Url Master 1.14.x (this is available from the Url Master product page).
If you have upgraded your DNN from 4.x to 5.1, you should upgrade to Url Master 1.14 as soon as possible.
Additionally, if you upgrade to DNN 5.1, and you already have the Url Master module installed, you will find that the Icons for the Page Urls and Friendly Url Settings pages are now broken in your menu system.
To fix this problem, go to your host->sql page, and copy/paste the following script into the sql screen
update {objectQualifier}Tabs
set IconFile = '~/images/' + IconFile
,IconFileLarge = '~/images/' + replace(IconFile, '16', '')
where IconFile in ('Friendly-Urls-Icon16.gif','Page-Urls-Icon16.gif')
update {objectQualifier}TabModules
set iConFile = '~/images/' + IconFile
where IconFile in ('Friendly-Urls-Icon.gif','Page-Urls-Icon.gif')
Check the 'run as script' box, and execute the sql. This will fix up the icon paths for the Url Master specific pages.
Also, you may wish to update the regex filters to the latest recommended values (if you haven't already modified them for your own purposes).
Here are the latest default values for Url Master 1.14 - you can update them through the Host->Friendly Url Settings page
ignoreRegex : (?<!linkclick\.aspx.+)(?:\.pdf$|\.gif$|\.png($|\?)|\.css$|\.js($|\?)|\.jpg$|\.html$|\.htm$|\.axd($|\?)|\.swf$|\.flv$|\.ico$|\.xml($|\?))
doNotRewriteRegex : /DesktopModules/|/Providers/|/LinkClick\.aspx
doNotRedirectRegex : /LinkClick\.aspx|/Providers/|/DesktopModules/
triggerDictionaryRebuildRegex : &ctl=tab|/ctl/tab|/Admin/Tabs/|/ctl/Signup
If you find any other DNN 5.1 related issues, please add to this thread.