Index was out of range. Must be non-negative and less than the size of the collection. (4250121)

After an In-Place upgrade of Active Roles, the following is observed in the Configuration Center after being prompted to upgrade the Web Interface sites configuration:

Unable to retrieve Web Interface site configuration objects.
Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: Index

The sites function normally, but the Configuration Center repeatedly prompts for upgrades.

Clear the IsInPlaceUpgrade flag in the Registry.

1. Launch the Registry Editor
2. Navigate to HKEY_LOCAL_MACHINE\SOFTWARE\One Identity\Active Roles\Configuration\Web
3. Set the IsInPlaceUpgrade DWORD to 0

​Restart the Configuration Center to verify issue resolution.