Some web apps require specific browsers. These web apps use what is called the "User Agent String" to identify which browser you are using and other information. Hana uses the same web and javascript rendering engine as Apple's Safari uses. This is a very modern renderer.
By default, Hana will tell any web app that asks that you are using Hana, a Webkit based application. Unfortunately, some web apps will still require another engine, such as that in Firefox or Internet Explorer.
If the web app will work with Safari and is still telling you that you need to use another browser, then all you have to do is switch that app's user agent string setting in the preferences to Safari from the Default or another browser. The page should reload shortly and the offending message should be gone.
In the event that the web app does not work with Safari or Hana, you can try, at your own risk, spoofing. (Go here to read more about spoofing.) We recommend trying Firefox and Camino first, then any other web browser on the Mac, then finally Internet Explorer for Windows. If it still doesn't work, you may be out of luck. We recommend and request that you let them and us know of your problem.