There was an issue in microsoft word web app can't open this document "Sorry,we can't open this document because there was a problem talking to the service"

Farm Information:

• Web Application published internally and externally (so make sure both URLs added to Alternate Access Mapping)
• Office Web Apps 2013 (Published externally via TMG 2010 and internally)

I have a farm which connected to Office Web Apps 2013 and It's working fine internally so then we decided to enable it to open Office Web Apps externally by the following steps :

1- In Office Web Apps Server , Open Power Shell and run this command to add the External URL to existing Farm:

Set-OfficeWebAppsFarm -ExternalURL http://test.com/

2-In SharePoint Server , Open SharePoint 2013 Management Shell and run the following commands:

Remove-SPWOPIBinding –All:$true

New-SPWOPIBinding -ServerName OfficeWebAppServer.com -AllowHTTP
Set-SPWopiZone internal-http
$c = Get-SPSecurityTokenServiceConfig
$c.AllowOAuthOverHttp = $true
$c.Update()

then when I tried to access the Office documents from External URL I got the following error :

"Sorry,we can't open this document because there was a problem talking to the service"

• This issue related to TMG publishing rule so to fix it :
• Open TMG Management Console
• Go to Publish rule for Office Web Apps
• Right click on the rule and choose Configure HTTP
• Uncheck  Verify Normalization
• Click ok
•  Click Apply
•  Wait the sync process

Ref:

http://technet.microsoft.com/en-us/library/jj204665.aspx

http://blogs.technet.com/b/dodeitte/archive/2013/11/10/issue-with-office-web-apps-server-2013-published-externally-using-tmg-2010.aspx