Can't export my document to PDF

[Alexandra]

I'm having problems exporting my LyX file to PDF. My problem is that this is 
the 
first time I've used LyX. The error messages are as follows: 
LaTex Error: \mathbb allowed only in math mode. 
[...ach\mathbb{Z_\mbox{\ensuremath{n}}}}.}} -You're in trouble here.]
Missing $ inserted. 
Extra }, or forgotten $. 
Extra }, or forgotten $.
Extra }, or forgotten $.
Missing } Inserted
Missing $ Inserted. 
Missing } Inserted
Missing } Inserted

Thanks for the help!