Confusing compiling error

[Maaneli Derakhshani]

Hi LyX Users,
I have been cut/pasting source code from a LyX document to a LaTeX document, 
and compiling the latter without difficulty until now. Out of nowhere, after 
the last pasting from LyX to LaTeX, I suddenly get a compiling error which 
doesn't go away when I undo the pasting. The GotoError button isn't helpful - 
it just highlights "\begin{document}" at the beginning of the TeX document. I 
have no idea what the problem is, so any help would be greatly appreciated. 
Regards,Max