1. Couple of threads here. Note issue of permissions as well as wacky characters in file name re Excel.
2. A quick fix sometimes is to be able to open the file and save it with a different name and never use the other one again.
3. From my own experience, the MS Office 2011 may have become corrupted.
By reinstalling Office 2011 you might be able to address these problems.
The current version of Office 2011 is 14.5.2
First - find your Office 2011 install disc with the product key # - and only then remove Office according to MS instructions
Or go here to DianefromOregon's site for help removing Office 2011:
then Reinstall from DVD
then enter your Product #
After successfully reinstalling Office 2011, update your Office product by going to the Help menu within Word or Excel or PowerPoint and select Update.
How to locate product keys
or here on locating product keys
This note is updated as of July 14, 2015