Unable to open the excel document using office web app, by accessing external URL. getting error (We're not able to contact the server. it might not be responding, or your internet connection may have been interrupted. Please try again)

Configuration Details:

1. SharePoint 2103 (Installed in windows server 2012 R2 Standard) last windows update runs on 24 Nov, 2014

2. Office web app version - 15.1.4481.1508 (Installed in windows server 2012 R2 Standard) last windows update runs on 14 Dec, 2014

after windows update on "Office web app server" we are not able to open any document in share point site, so we re-configured office web app, now everything works fine in Internal and External Network except Excel document which is not working when accessing from External network.

Is the WAC URL available externally? Clients need to be able to talk directly to WAC as well.

Hi,

To resolve this problem, the administrator must grant access to the account to run the Excel Services Application.  To do this, follow these steps for each Web application:

1. Click Start, click All Programs.
2. Click Microsoft SharePoint 2010/2013 Products.
3. Click SharePoint 2010/2013 Management Shell.
4. At the Windows PowerShell command prompt (PS C:\>), type the following command, and then press ENTER:
   
   PS> $w = Get-SPWebApplication Identity <<var>URL of the Web application</var>>
   PS> $w.GrantAccessToProcessIdentity("<<var>insert service account</var>>")
   
   Note The placeholder <insert service account> represents the service account that you use to run the Excel Services Application.

After you do this, the service account is granted db_owner access to the SharePoint content databases.

@Will Ho

we are not using Excel service to render the workbook, Excel Web App is used to render the workbook.

@Trevor Seward

Yes it is accessible externally, except Excel, Word and Power point are opening in browser. while opening Excel in IE - 11 i am getting this error "We're not able to contact the server. It might not be responding, or your internet connection may have been interrupted. Please try again", in other browser it keeps on loading work book will not be opened.

was this issue ever resolved

Still we dint fix the issue. If you have any suggestion to fix the issue kindly share, i will try and let you know.