ArcGIS Pro may crash on startup after upgrading to Pro 2.8, crashing with the exception "System.MissingFieldException" and the message "Field not found: 'Lucene.Net.Analysis.StopAnalyzer.ENGLISH_STOP_WORDS_SET'."

Description

After upgrading to version 2.8, ArcGIS Pro may crash on startup on machines that have the .NET 3.5 version of Lucene.net v3.0.3 registered in the .NET Global Assembly Cache (GAC), and the exception "System.MissingFieldException" and the message "Field not found: 'Lucene.Net.Analysis.StopAnalyzer.ENGLISH_STOP_WORDS_SET' is returned.

Lucene.net is a popular open source search library used by both Esri and non-Esri applications.

This has been logged as BUG-000139936.

Cause

The crash is due to a conflict between the copy of Lucene.net.dll in use by ArcGIS Pro, and a similar copy registered in the GAC by some other application. It is not yet known which application or applications are registering the conflicting version of Lucene in the GAC on impacted machines, but Esri has confirmed that neither ArcGIS Pro nor ArcMap register Lucene v3.0.3 in the GAC. The .NET framework prevents this type of DLL conflicts by allowing DLL authors to uniquely name and version DLLs when their contents change. However, the Lucene.net library was not authored in a way that allows for the conflict to be easily detected.

Workaround

Warning:   
The instructions below include making changes to essential parts of your operating system. It is recommended that you backup your operating system and files, including the registry, before proceeding. Consult a qualified computer systems professional, if necessary.

Esri cannot guarantee results from incorrect modifications while following these instructions. Therefore, use caution and proceed at your own risk.

1. Open regedit.exe and browse to HKEY_CURRENT_USER\Software\ESRI\ArcGISPro\Settings.
   This folder may not exist if the computer has never had ArcGIS Pro installed.
2. Create a new DWORD (32-bit) Value, and name it CommandSearchEnabled.
3. Verify that the Data column for CommandSearchEnabled says 0x00000000 (0). If the value is something other than that, set it to 0.

ArcGIS Pro 2.8 should now start without crashing. However, the new Command Search functionality will not be available until a later patch.

Steps to Reproduce