Came across and issue during the deployment of Office Web Apps 2013 when hooking up with SharePoint which caused some confusion.
Error messages from the web apps when activating through SharePoint documents:
Word Document : "Sorry, there was a problem and we can't open this document. If this happens again, try opening the document in Microsoft Word."
Excel Document: "We couldn't find the file you wanted. It's possible the file was renamed, moved or deleted"
PowerPoint: "Sorry, we ran into a problem. Please try again"
One Note:"Sorry, you don't have permission to edit this notebook."
It appears the issue was related to Office Web Apps having been deployed on HTTPS while SharePoint was on HTTP.
This is mentioned in the tech net documentation but it wasn’t very clear as it appeared to be the opposite way around, but the resolution is to allow SharePoint to use OAuth authentication over http instead of https (thanks to Imp44 for the solution at TechNet Forums )
The solution is to run the following on a SharePoint 2013 Server:
$config = (Get-SPSecurityTokenServiceConfig) $config.AllowOAuthOverHttp = $true $config.Update()