An application designed using DNN 9.1.1 Evoq is showing a
500 - Internal server error page when opening a notification detail link. The error message details in the URL points to "Object reference not set to an instance of an object".
By investigating the log files, an error related to a control file that "does not exist" in a given path is found being logged at the same timestamps of the "Internal Server Errors". It references a specific skin source theme file (in this case, this was "Dark-Knight"), associated there to the tab numbered as 63, as below.
The error can be resolved by the following steps::
1. Go to Persona Bar > Settings > SQL Console.
2. Locate the table row that identifies the reference within table TABS by running query
SELECT * FROM tabs WHERE tabid = <tab-number-identified-in-logs>.
3. Clear the reference to the file related to the skin source theme in the problematic tab, by running the command:
update tabs set SkinSrc = null where tabid =<tab-number-identified-in-logs> (that was 63, in this case).
4. Go to Persona Bar > Settings > Servers to access the Server Configuration screen.
5. Hit buttons Restart Application and Clear Cache.
Note: This step results in temporary downtime for the application, so you may want to ensure this is done in a more desirable time, typically out of business hours for a production environment.
6. Reload the application in your browser and validate that the problem is gone, by clicking the link to the notification page.