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)
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.