Issue

Following an upgrade to Snow License Manager (SLM) 9.30, the application is inaccessible and displays HTTP Error 500.19:

Analysis

Downgrading and running the upgrade again has no effect. 

Examining the detailed error information, the Config Error provides greater insight as to what's happening:
 

Resolution

This message indicates that the upgrade created a duplicate entry in the web.config file. Removing the duplicate entry resolves the issue.

1. Open the config file referenced in the detailed error information using notepad++ or other text editor.
2. Remove the duplicate row and resave the file. 
3. Refresh the browser and attempt to access SLM again. You may need to clear your browser cache.