Richard Heck answered this question on the lyx-users mailing list in this thread:
I think you get this error if you do not have a layout file for whatever class the template uses. In this case, the class is bmcart.layout
, and unless you wrote a layout file yourself, you do not have one.
Please see Chapter 5 of the Customization manual for information on what layout files are and so forth, if that did not make sense to you. Since bmcart is just a variant of article, you should at least be able to get basic functionality by
(i) copying the article.layout
file into your LyX user directory;
(ii) renaming it as bmcart.layout
;
(iii) changing the first line to read:
\DeclareLaTeXClass{Article (BMC)}
(iv) reconfiguring LyX and then attempting to re-import.
Probably a lot of the template will import as ERT, since this layout file says nothing about whatever is different about bmcart.