Spaces and some other fonts are changed to rectangles

I installed Microsoft Office 2011 yesterday on my MacBook Pro with Snow Leopard. I already had Microsoft Office 2008 on this device and simply added 2011. Now for some reason, many of my fonts have changed to rectangles as if I don't have the fonts installed. Also when I am in Mac Mail, the spaces are replaced with rectangles with "A" inside of them.

How can I fix this? Has anyone had a similar experience?

If you need more information from me, feel free to comment.

SOLVED:

I used the Terminal command:

sudo atsutil databases -remove; sudo atsutil server -shutdown; sudo atsutil server -ping

This cleared the cache and resolved the problem.

You could also use Lion Cache Cleaner or CleanMyMac to clear the cache and restore all the fonts.

NOTE: Make sure to open the "Font Book" application and make sure you resolve all duplicate fonts. Right-Click on the fonts with a small yellow attention sign beside it and click "Resolve Duplicate". This can also cause problems.

Gave credit to @da4 and @lri for there answer.