Consider a scenario where the UAG administrator just published OWA located on an Exchange Server 2010 and when external users click the OWA link from the portal they get the following page:
They users are able to access OWA internally without any problem and before implementing Exchange 2010, the users were able to access OWA using Exchange 2007.
Reviewing the Web Monitor log it is possible to notice the following errors:
As you can see the error message that is highlighted above says that the application Exchange 2010 of type ExchangePub2007 failed. This means that when the administrator created the Exchange publishing rule within the trunk he selected the wrong Exchange version (or in this case he just used the same application in the portal after replacing Exchange 2007 to Exchange 2010). This option is available on step 2 of the add application wizard as shown below:
When publishing Exchange through UAG 2010 make sure to choose the correct version on step 2 of the Add Application Wizard and if you currently have a trunk that is publishing Exchange 2007, do not change the rule to point to a new Exchange 2010 Server, you will need to create a new application publishing within the trunk to publish Exchange 2010.