The IIS based websites throw error 500 when browsing. Each website on the service node is affected.
Each second the IIS related errors appear in Event Viever (Event Viewer > Windows Logs > Application):
Could not load all ISAPI filters for site 'EXAMPLE.COM'. Therefore site startup aborted.
The HTTP Filter DLL D:\ISAPIFilter\isapi_redirect.dll failed to load. The data is the error.
Invalid DLL is included in the list of servers ISAPI filters. All the websites inherit it and therefore fail to load.
Remove the DLL mentioned in Event Viewers error from the list of servers ISAPI filers (IIS > Server_Name > ISAPI Filters)