Solution: SAP note 1347768
1. Change configuration of supported clients.
a) Open Visual Administrator. On the relevant server instance, navigate to "Services -> Configuration Adapter". In the detail view, a tree becomes visible. Navigate to "webdynpro -> sap.com -> tc~wd~dispwda -> "Propertysheet clients". Open this propertysheet in edit mode by pressing the "Edit" button on the toolbar.
b) Change following property in the propertysheet wizard.
Default value is: "MSIE 6."
change custom value to: "MSIE" and click 'Apply custom' button.
c) Having done this, close the wizard and press again the "Edit" button to save the changes. Afterwards, a restart of the engine is required in order to make these changes effective. The WebDynpro runtime should now be able to allow the usage of Microsoft IE8 browser.
2. Change the compatibility view settings in IE8 browser.
a) In the browser, Go to menu Tools -> Compatibility View Settings.
b) Select the checkbox "Display all websites in Compatibility View" and click on the 'Close' button.
c) Close all browser sessions and then open a new browser window. The WebDynpro runtime should now be able to allow the usage of Microsoft IE8 browser.