Office Web Apps SharePoint 2010 error: Word Web App cannot open this document due to an unknown error. If the problem persists, try opening the file in Microsoft Word.
After installing Micrsooft Office Web Apps and then deactivating it, users have been reporting problem when attempting to open Word documents. Users would generally receive the following error message: “Word Web App cannot open this document due to an unknown error. If the problem persists, try opening the file in Microsoft Word.”
There are two features that need to be activated and deactivated at the Site Collection level.
1. Ensure Office Web Apps is deactivated.
2. Ensure that Open Documents in Client Applications by Default has been activated.
You should now be able to access content through the client applications by default.