Hi,
This error is caused by a Newtonsoft.Json assembly version mismatch in the Dynamics 365 on-premises installation.
The error:
Could not load file or assembly 'Newtonsoft.Json'...
The located assembly's manifest definition does not match the assembly reference.
HRESULT: 0x80131040
usually occurs when the CRM binaries and the installed Newtonsoft.Json DLL versions are no longer consistent.
According to Microsoft's guidance, this can happen particularly when upgrading from later Dynamics 365/CRM 9.0 builds to an older 9.1 update. Microsoft notes that if the 9.0 deployment is 9.0.47.08 or later, you should upgrade directly to 9.1.20.11 or later to avoid assembly/file versioning issues.
I would recommend the following:
- Do not manually add random Newtonsoft.Json DLLs to the GAC, as this may create additional version conflicts.
- Check the Dynamics 365 installation folders, especially the Tools folder, for the installed Newtonsoft.Json.dll version.
- Upgrade the Dynamics 365 server to 9.1.20 or a later supported update.
- If the installation is already in an inconsistent state, a clean reinstall of the CRM server binaries may be required. Before reinstalling, make sure the old Dynamics 365 installation folder is completely removed, while keeping proper backups of the CRM databases and configuration.
A Microsoft employee also confirmed in a similar Community thread that the generic solution for Newtonsoft.Json mismatches may require reinstalling CRM and ensuring old Dynamics 365 binaries are removed first.
Also, avoid uninstalling CRM patches to downgrade versions, because uninstalling a patch does not necessarily restore all DLL versions or downgrade the database schema correctly.
Hope this helps.