I did install it and reconfigured it. But the RTF-Export is still not present.I believe that there is also an option to export as rtf.Not in my 1.4.3on Ubuntu Lyx-Qt. What program is used for that export? Maybe I missed to install it...You need latex2rtf at http://latex2rtf.sourceforge.net/
Could anyone using Ubuntu reproduce this? Thanks for your help. Tim