Can you try this:
1. exit LyX
2. back up any folder that starts ~/.lyx
3. remove any folder that starts ~/.lyx
4. start LyX
5. Can you now export either through the buttons or from File > Export ?
note that to copy and remove you can do something like
mkdir ~/Desktop/lyxBU &&
cp -r ~/.lyx* ~/Desktop/lyxBU &&
rm -rf ~/.lyx*
OK so LyX has no trouble finding LaTeX it seems.
Can you try this:
1. exit LyX
2. back up any folder that starts ~/.lyx
3. remove any folder that starts ~/.lyx
4. start LyX
5. Can you now export either through the buttons or from File > Export ?
note that to copy and remove you can do something like
mkdir ~/Desktop/lyxBU &&
cp -r ~/.lyx* ~/Desktop/lyxBU &&
rm -rf ~/.lyx*