What to do if Office Web Apps (OWA) Stops Working in SharePoint

A customer ran into this issue a while back a couple of times and I wanted to document it for others. The customer was using their SharePoint environment normally throughout the day when all of a sudden their Office Web Apps stopped working. As it turns out, the ultimate problem ended up being related to a timer job that wasn’t running properly, but we did find a work around while looking for that. Below is a description of the workaround.

If you’re seeing something along the lines as this in your Excel Web App (Server Error in ‘/x’ Application).

And if your event logs have something along the lines of this in them.

Where the details look like this below.

The Workaround

Then you can run the following PowerShell command (in an elevated PowerShell console) to correct the problem.

Update-SPWOPIProofKey

The above is just a work around, and the following is a description of the problem in more detail.

A quick look at the SPWOPI actions revealed this was a possible solution.

PS C:\Users\spadmin> get-help *spwopi*

Name                              Category  Module                    Synopsis

—-                              ——–  ——                    ——–

Get-SPWOPIBinding                 Cmdlet    Microsoft.SharePoint.P… Applie…

New-SPWOPIBinding                 Cmdlet    Microsoft.SharePoint.P… Applie…

Remove-SPWOPIBinding              Cmdlet    Microsoft.SharePoint.P… Applie…

Set-SPWOPIBinding                 Cmdlet    Microsoft.SharePoint.P… Applie…

Get-SPWOPIZone                    Cmdlet    Microsoft.SharePoint.P… Applie…

Set-SPWOPIZone                    Cmdlet    Microsoft.SharePoint.P… Applie…

Get-SPWOPISuppressionSetting      Cmdlet    Microsoft.SharePoint.P… Applie…

New-SPWOPISuppressionSetting      Cmdlet    Microsoft.SharePoint.P… Applie…

Remove-SPWOPISuppressionSetting   Cmdlet    Microsoft.SharePoint.P… Applie…

Update-SPWOPIProofKey             Cmdlet    Microsoft.SharePoint.P… Applie…

Simply running this command on the PowerShell command line (on the SP server) resolved the issue with previews not being generated at the client (note the OWA farm looked OK on the OWA server).

Update-SPWOPIProofKey Detailed Description

The Update-SPWOPIProofKey cmdlet updates the public key that is used to connect to the WOPI application (which could be a server that runs Office Web Apps Server) on the current SharePoint farm where this cmdlet is run. You may want to use this cmdlet if the keys become unsynchronized between the SharePoint farm and the WOPI application. If the keys are unsynchronized, documents may not open in the browser and messages such as “Invalid Proof Signature for file…” or “Invalid Proof Signature for folder…” are found in the Unified Logging System (ULS) logs.

Here’s what was Really Happening at the Customer’s Site:

The root of the issue was as follows.

This timer job, which was scheduled to run every half hour, hadn’t run in months. In our case, the entirely server was screwed up (we eventually replaced the server, and rebuilt the AppFabric Cache on a new set of servers, and then the SharePoint Timer service started running properly again, including this job).

The ProofKeys change regularly, and as such, can be become out of date between SharePoint and the Office Web Apps server. Normally, this timer job (properly running on schedule) would be sufficient to automatically obtain the new keys.

ProofKeys Detailed Description

ProofKeys change regularly on the Office Web Apps server. Use Update-SPWOPIProofKey to update them on SharePoint. Alternatively, change the timer job schedule with:

set-SPTimerJob “job-rerun-discovery” -schedule “<your desired schedule>”