Thanks, Craig, for the info. I've removed the Font Awesome JS reference and can still see the icons, so that's good.
The bad news is that I still get the error posted in my initial post. Not sure what's causing it now. The only thing I thought each page with the error had in common was using Font Awesome, but it must be something else. I even removed all references to Font Awesome and still got an error.
I have a work-around, so it's not the end of the world, just a little annoying.
I also get this error, but for the \rdsdbdata\db directory. We're running MySQL on Amazon RDS. I'm guessing Mango does not have permissions to view the file system, or is treating \rdsdbdata\db as a local directory when trying to view the usage?
As Fox asked, any way to disable this check to save some errors in the log file?