Our CRM instance got update an update this weekend (version 1710 (9.1.0.10334), gcc region) and since than we can't register new plug-in assemblies or update existing.
Error is:
ERROR: Exception retrieving custom activity info using SandboxWCFMethod - Unhandled exception: Exception type: Microsoft.Crm.CrmNotSupportedException Message: This action is not supported. at Microsoft.Crm.Sandbox.SandboxCustomActivity.GetSandboxCustomActivityInfo(ActivityInfo activityInfo, Guid organizationId)
It looks really similar to this issue: https://community.dynamics.com/crm/f/microsoft-dynamics-crm-forum/253106/registering-a-custom-workflow-activity-using-plug-in-registration-tool
So I guess it comes from SDK version mismatch.
But which SDK assemblies versions am I supposed to use with this CRM version?
Latest I see in NuGet is 9.0.2.21 with comment "Updating for 9.1.0.10129" which doesn't work for us.