HTtrack is not aware that certain names (of both files and directories) are
forbidden under windows and tries to create them giving rise to serialize
errors.

These names are CON, PRN, AUX, NUL, COM1, COM2, COM3, COM4, COM5, COM6, COM7,
COM8, COM9, LPT1, LPT2, LPT3, LPT4, LPT5, LPT6, LPT7, LPT8, and LPT9, both
alone and when followed by a point EVEN WHEN IT IS NOT THE LAST POINT OR FOR
FOLDER NAMES. So, for example, con.members-here.com is not accepted as either
a file or a folder name.
To avoid the problem you might just add a character such as X after the
reserved name, when it is forbidden, or escape a part of it.

There might be other violations, I didn't try everything, you should check
here:
<http://msdn.microsoft.com/en-us/library/windows/desktop/aa365247%28v=vs.85%29.aspx>
and pass all the file and folder names through a function that sanitizes them,
at least under Windows.