Hi!

Although we are not very proficient in DNN, we think the issue you may have is caused by DNN saving the base URL somewhere in it's configuration - either in a database or in some config file. Please refer to DNN support community sites to find where exactly that settings is stored. To make UltiDev Cassini easier to use for DNN developers, we recommend doing two things while installing DotNetNuke:
1. When registering DNN with Cassini, make sure Keep in Application In Memory flag is turned off until application was completely installed and configured. With that flag on DNN will not install correctly. After you finished installing and configuring DNN, you can turn on Keep Application In Memory flag if you wish.
2. When pointing your browser to DNN for the first time, use the same base URL as everyone else will be using. For example, if your users will access your application at http://dnn.contoso.com:1234/Home/tabid... etc, you will need to run DNN for the first time using the same base http://dnn.contoso.com:1234/ URL, and not http://localhot;1234. The reason for that is above-mentioned feature of DNN - where base URL is stored as a part of configuration.

Please let us know if you were able to resolve the issue.

Best regards,
UltiDev Team.