Hi,
The Original exception is being thrown by the Plugin,
System.ServiceModel.FaultException`1[Microsoft.Xrm.Sdk.OrganizationServiceFault]: User List does not contains record or contains more than one record with same Id. Please resolve the issue to continue. (Fault Detail is equal to Exception details:
ErrorCode: 0x80040265
Message: User List does not contains record or contains more than one record with same Id. Please resolve the issue to continue.
TimeStamp: 2020-03-03T14:44:07.8526285Z
OriginalException: Microsoft.Xrm.Sdk.InvalidPluginExecutionException
at SmithAndWilliamson.Plugin.CreateConnection.Execute(IServiceProvider serviceProvider)
SandboxPlugin.Execute: CrmException: SmithAndWilliamson.Plugins, Version=1.0.0.0, Culture=neutral, PublicKeyToken=ed3b9c1342acd6db; -2147220891; Microsoft.Crm.CrmException: User List does not contains record or contains more than one record with same Id. Please resolve the issue to continue., Context: SandboxCodeUnit.Execute, TrackingId: f7697e78-19ad-48ee-a5c3-5493e860cd10, ExecutionId: c1c6c4d3-2a77-c57b-d450-691b6cca8fbf, Depth 1
- I agree with Andrew, test by deactivating the plugin and troubleshoot the code to fix the issue.
Please mark this comment as suggested answer if this answers your query.