Does it occur also in outlooks safe mode?
Running Outlook 2010 on Windows8
Receiving and initiating emails works fine but unable to forward or reply to them.
For example: an attempt to forward an email causes a supplemental window titled "FW: xxxxxxxx Message (Plain Test)" to open. But then nothing happens, nor is there any error message. It just sits there indefinitely. It appears to be active (the Title bar is blue) but nothing changes and any/all attempts to click on it are ignored. This means it can't be 'X'd out, nor can it be returned to the main window. The only way to proceed is to use Task Manager to terminate the Outlook program.
Problem appeared following automatic update of Windows8 to Windows 8.1