Troubleshooting Tip: Windows Agent Show Registered but no Event Upload. System.MissingMethodException error

[froslan]

Description

This article explains the steps to resolve the System.MissingMethodException error observed in Trace.log when the Windows Agent is registered in the FortiSIEM GUI, but no events are being uploaded.

Scope

FortiSIEM.

Solution

1. Windows Agent shows as registered in the FortiSIEM GUI, but no events are being uploaded. System.MissingMethodException error is observed in Trace.log:

2025-08-04 14:43:49,486 [1] ERROR FortiSIEM.Webproxy.AOWebService - NotifyStatusV2 exception
System.MissingMethodException: xxxx:“System.Collections.Generic.HashSet`1<!!0> System.Linq.Enumerable.ToHashSet(System.Collections.Generic.IEnumerable`1<!!0>)”。
x FortiSIEM.Webproxy.SuperManager.Notify(String action, String message, String jobs, UInt64& lastUpdate, Boolean& fActive, Boolean& FINS, String& template, AOCollector[]& collectors, MarshalledTask[]& tasks)
x FortiSIEM.Webproxy.AOWebService.NotifyStatusV2(AONotifyExV2& aoNotify)

2. This issue occurs because the Enumerable.ToHashSet() method is not available in .NET Framework versions earlier than v4.7.
3. Upgrade the .NET Framework on the affected Windows Agent server to v4.7 or later and reboot the system.