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I don't think so. The problem is that \selectlanguage{english} command is set in the source you provided (immediately after \begin{document}), but babel package isn't loaded at all (and all errors are babel-related). So, either go to Document > Settings > Langauge and set the language or put into ...

I can't see how a kernel upgrade can have any impact on LaTeX. Please, post here an example .lyx file which shows the problem.

I think that the problem is here:

(/usr/share/texmf-texlive/tex/generic/oberdiek/ifpdf.sty
Package: ifpdf 2009/04/10 v2.0 Provides the ifpdf switch (HO)
Package ifpdf ...

thanks for your reply.
Here is the Latex source:
% Preview source code

%% LyX 1.6.5 created this file. For more info, see http://www.lyx.org/.
%% Do not edit unless you really know what you are doing.
\documentclass[12pt,a4paper]{article}
\usepackage[]{fontenc}
\usepackage[latin9]{inputenc ...

hello everyone.
I'm working on the Ubuntu 10.04 & Lyx 1.6.5. Then I upgraded my kernel to version 2.6.32 - 26 several days ago. Then everything seems wrong, the Lyx cannot DVI or make pdf even the tutorial file in Help -> Tutorial. Here is the err information:
Package babel Error: you haven't loaded ...