Reenable support for BDC model system type DotNetAssembly and WebService

Starting with the September 2024 Cumulative Update (CU), SharePoint no longer supports importing new BDC models based on the LobSystem types DotNetAssembly and WebService.
Beginning with the June 2025 CU, previously imported BDC models using these system types are also disabled.

These or similar errors are returned when trying to use this BDC system type:

System.InvalidOperationException: DotNetAssembly/WebService system type is not supported.

System.InvalidOperationException: The Model contains LobSystem (External System) of Type ‘DotNetAssembly’ which is not supported.

The recommended migration path for customers using these LobSystem types is to migrate to one of the other supported LobSystem types.

The most common migration path is WCF. This requires creating a new WCF service hosted on a web server that implements the methods required by the BDC model. The business logic of the WCF service can mostly be copied from the existing DotNetAssembly/WebService implementation.

To support customers who need time for this migration and currently rely on these LobSystem types, the August 2025 CU for SharePoint Server (2016, 2019 and Subscription Edition) introduces an option to re-enable them.

Run this PowerShell script in a SharePoint Management Shell to enable DotNetAssembly LobSystem type:

$farm = Get-SPFarm
$farm.ServerDebugFlags.Add(57007)    # Enabled DotNetAssembly system type
$farm.update()

Run this PowerShell script in a SharePoint Management Shell to enable WebService LobSystem type:

$farm = Get-SPFarm
$farm.ServerDebugFlags.Add(57008)    # Enabled WebService system type
$farm.update()

After the change has been applied the relevant service which uses this BDC model has to be restarted. This can either be IIS or the SharePoint Search Service.