Knowledge Base

Resolving “503 Service Unavailable” responses caused by a corrupted IIS Rewrite module

Applies To

Proton 4.0+


Proton Server can enter a state where a user will see a “503 Service Unavailable” response. This can happen when the IIS Rewrite module (rewrite.dll) becomes corrupted. This can be resolved by deleting the module and reinstalling it.


To verify you are seeing 503 Service Unavailable responses as a result of a corrupted IIS Rewrite module you will need to look for IIS errors in your Event Viewer logs. You will find these errors in the “Windows Logs\Application” location with “Microsoft-Windows-IIS-W3SVC-WP” as the source. The following is an example error.

Log Name: Application Source: Microsoft-Windows-IIS-W3SVC-WP Date: 5/30/2017 1:28:49 PM Event ID: 2280 Task Category: None Level: Error Keywords: Classic User: N/A Computer: TestMachine Description: The Module DLL C:\WINDOWS\system32\inetsrv\rewrite.dll failed to load. The data is the error. Event Xml: <Event xmlns=""> <System> <Provider Name="Microsoft-Windows-IIS-W3SVC-WP" Guid="{670080D9-742A-4187-8D16-41143D1290BD}" EventSourceName="W3SVC-WP" /> <EventID Qualifiers="49152">2280</EventID> <Version>0</Version> <Level>2</Level> <Task>0</Task> <Opcode>0</Opcode> <Keywords>0x80000000000000</Keywords> <TimeCreated SystemTime="2017-05-30T17:28:49.934177500Z" /> <EventRecordID>31998</EventRecordID> <Correlation /> <Execution ProcessID="0" ThreadID="0" /> <Channel>Application</Channel> <Computer>TestMachine</Computer> <Security /> </System> <EventData> <Data Name="ModuleDll">C:\WINDOWS\system32\inetsrv\rewrite.dll</Data> <Binary>7E000000</Binary> </EventData> </Event

To resolve this issue you will need to delete the rewrite.dll module. On a default IIS installation this file is located at %windir%\System32\inetsrv. You should stop IIS before attempting to delete this file. Once you’ve deleted the module you will need to reinstall it by downloading the Web Platform Installer from Microsoft. Once you have the Web Platform Installer running you will need to navigate to the “Products” tab and scroll down until you find “URL Rewrite 2.0”. Click “Add” and restart IIS once the installation is complete.

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