.info file having a name that is different from the name of the theme's folder My .info file is prosperpro.info, but my theme's folder is named prosperpro8. I had not realized this difference because the code was working. When I realized this, and tried to changed the .info file back to prosperpro8.info, the code would no longer work.

I thought that the .info file required to have the same name of the theme's folder.

Am I wrong? If they must have the same names, how can I correct it? (Changing the file name will result in code break.)
You cant give same name for theme and module. 
I have found an article on drupal.org


  How to Resolve module-theme name collision
  
  When developing a site it can happen that a module and theme are being
  given the same name. This results in very weird behavior: overriding
  hooks can make your blocks disappear, print $content returns only
  'array', hence disappearing admin interfaces which force us to alter
  the database to get back on track.
  
  Now we have to find out how to remove the new theme and switch back to
  an old one. if your site is big, with lots of content, then
  reinstalling is not an option. I tested this with MySQL, so these
  hints are for MySQL only.
  
  Make a backup of your database first. We are going to edit the dumped
  records, and reinsert the database. I used this method because using
  my favorite editor is way easier and safer than using MySQL shell
  (anyway we shouldn't edit a live site database).
  
  The theme name is registered in the following tables in your database:
  system, variables and block. Clear the cache manually, meaning to
  remove all the INSERT INTO cache_ lines in order to see results.
  Change the 'default_theme' value in system. Note that 's' stands for
  string length, so be sure you put the string length after the 's:'.
  Also make sure you change the value to an existing theme (available
  themes are listed in system). And remove, or rename your troublesome
  theme.
  
  The change in block is imperative, otherwise the blocks will not
  appear. Drop your old database from the sql server and insert the
  edited one. Voila, we have recovered from a theme crash.


© drupal.org

And

Never give a module and a theme the same name 

Here's the D7 Patch