You can't put a \chapter or \addtocomments command in your preamble. That's why you're getting the error. These commands go in the document itself.
What you want to do here, I think, is put \addtocontents{toc}{\protect\mbox{}\protect\hrulefill\par} as ERT immediately following the chapter title in the LyX file. The \chapter command is already there, in effect: It's created by the Chapter "environment" in your LyX file. The titlesec/titletoc and tocloft packages are the ones you want. Whether you use titletoc or tocloft, well, that's a matter of personal preference, mostly. Richard Kamran SHAFQAT wrote: > Hi, > I am trying to write my thesis using lyx (koma-script report class). > But i would like to format the toc, lof and lot to have something like > the table in attachment. I tried to make use of tocloft and just > having a look at titlesec/titletoc package but i am not sure if this > is the best solution available. > > The following commands are mentioned in the manual of tocloft to add a > horizontal line across the whole width of the ToC below an entry for a > Part > > \part{Part title} > \addtocontents{toc}{\protect\mbox{}\protect\hrulefill\par} > > > i tired to put this in the preamble with Part tile replaced by title > of first chapter of my document but i got error saying > > [EMAIL PROTECTED] already define ....... > > can someone please have a look at the attachment and provide me some > hint or the package that could be used for this. > > formating thanks for all the help > > > regards, > > > Kamran