Error after SCOM integration: "Exception occurred in SimpleListenerExample.ProcessRequest while parsing XML" (4258300)

After setting up SCOM integration the following error appears in the Foglight event log:

Exception occurred in SimpleListenerExample.ProcessRequest while parsing XML: System.ArgumentOutOfRangeException: StartIndex darf nicht kleiner als Null sein. [Translation: StartIndex should not be less than null]
Parametername: startIndex
at System.String.InternalSubStringWithChecks(Int32 startIndex, Int32 length, Boolean fAlwaysCopy)
at XML_Rec_log.SimpleListenerExample.ProcessRequest(HttpListenerContext context) in C:\Quest_Software\Foglight\Integration\integration_trunk\src\integration-samples\forward-alarms-from-foglight\opsmgr-direct\XML-Rec-Log\XML-Rec-log\SimpleListenerExample.cs:Zeile 79.