LyX ⇒ Cannot edit latex

[hardya]

V Newbie Latex and lyx

I have changed document class through the document settings dialog.

Now when I compile to pdf I get an error message refering to a line of latex. I search for the latex in the document and it cannot find it, although some latex appears in the document as inserts, these appear to be mostly comments (%).

However I can find the line in the source but I can find no way to edit it. Also it appears to be a comment (%) and so I am confused why it is affecting the compilation!!

Error is:

\ifCLASSINFOpdf

The control sequence at the end of the top line
of your error message was never \def'ed. If you have
misspelled it (e.g., `\hobx'), type `I' and the correct
spelling (e.g., `I\hbox'). Otherwise just continue,
and I'll forget about whatever was undefined.

One thing that I have noticed is that there is something called the latex preamble but although it appears to resemble a whole load of comment at the top of your existing latex file, some little things are different for some reason and these are often the things that raise the errors, but in the latex source they are shown as commented out!! I really don't understand this.

Any help or advice greatly appreciated.

[meho_r]

It would help if you're able to attach the LYX file here (you may remove most of the text and replace the real text with some dummy one, the important thing is that error still occurs when you try to compile the document). Also, you'll have to put LYX file into a ZIP archive prior to attaching it here.

BTW, which document class are you using now and which one was in use before the change?