I'm trying to do the data import wizard exercise (https://developer.salesforce.com/trailhead/force_com_admin_beginner/data_management/data_import) and I'm getting the above error when I choose the file Trailhead tells me to download.  I went searching in the forums for an answer to this and tried the one suggestion -- copying to a notepad app and re-importing into excel.  It didn't work.  The other "suggestion" is to change browsers.  I don't find this an acceptable alternative.  In addition to the time and hassle it will take to shut everything down and fire it all back up in another browser, I don't have appropriate security set up on IE and I don't trust Chrome at all.  I also can't ask my users to do that every time they want to import. 

I've already been using the DataLoader and, where possible, DemandTools to import data.  I thought this would be a chance to learn how the Import Wizard works.  But all this exercise tells me is what other folks have told me before -- the Import Wizard is a pain and they don't use it. 

I don't expect the Trailhead forum to fix this, but I am about to load the required data using DataLoader.  I hope the Challenge doesn't care how I loaded it.  I will report back.  But in the meantime if anyone has any useful suggestions, please chime in.  Thanks.