With the new "Advanced" UrlFormat option in DNN 7.1 you might run into problems if your old website was using any URL Rewriting that replaced Spaces with anything other than a hyphen. If you want to replace the Hyphen with something else, such as an Underscore, than you can follow the directions in this tutorial. You will need to "override" the URL settings in DNN 7.1 to add additional options. In the DNN Platform, you have to do this manually, via the database, I believe the EVOQ ($paid$) versions have a UI for this, but for those of us who focus specifically on the open source platform, you need to make manually update database entries to customize the URL handling in 7.1+.

You'll want to add a HostSetting (or portal setting if you wish, but I won't provide the SQL for that) that defines the AUM_ReplaceSpaceWith setting. Here is a sample SQL script that will do that. (as always, run at your own risk, backup before executing, I'm not responsible for you screwing up your website).

insert into {databaseOwner}{objectQualifier}hostsettings
, SettingValue
, SettingIsSecure 
, CreatedByUserId
, CreatedOnDate
, LastModifiedByUserId
, LastModifiedOnDate
, 0
, -1
, -1

You can run this from the HOST/SQL window, or if you want to run it via SSMS, replace the {databaseOwner} and the {objectQualifier} tokens with the settings you have in your web.config. After executing this SQL you will need to recycle your application pool and clear the cache.