Encrypt an encrypted file?

I've just encrypted a few Excel files using the Protection feature built into Microsoft Excel 2010. It Encrypts the file and requires a password to open the file.
I have been planning on using Truecrypt Whole Disk Encryption on my laptop drive - as is required by my employer.

What might happen when Truecrypt goes to encrypt the Excel files that are already encrypted?? will it work or will it crash ??

 

It'll work.