Upgrade from ArcGIS Enterprise 11.5 to versions 12.0 or 12.1 fails when the Portal for ArcGIS 11.5 Security 2026 Update 1 Patch is installed on Windows

If the Portal for ArcGIS 11.5 Security 2026 Update 1 Patch is installed, do not upgrade ArcGIS Enterprise 11.5 environments on Windows to versions 12.0 or 12.1 or uninstall the Portal for ArcGIS software until the corrected patch is installed.  In the Patch Notification Tool, the corrected version appears as Portal for ArcGIS Security 2026 Update 1 Patch with a release date of June 4, 2026. After installation, it is listed as Portal for ArcGIS Security 2026 Update 1 Patch D. This updated patch must be installed to replace earlier versions of this patch before upgrading ArcGIS Enterprise.

If you have questions, please contact Esri Technical Support.