For all people that experience panic about
Illegal mix of collations
while some programming process between database mysql and php.
To solve, manually and without third party plugin or additions, you can do this simple procedure (it is necessary to have at least a good text editor like uedit or similar to proceed speedy and without errors with this simple (but effective) procedure):
  1. download your database
  2. open the file with text editor
  3. search for all lines containing "COLLATE=latin1_general_c s" ( latin1_general_cs was my used collate charset, you need to set your )
  4. substitute all COLLATE=latin1_general_cs with COLLATE=utf8_unicode_ci
  5. search for CHARSET=latin1 and substitute with CHARSET=utf8 (latin1 was my charset you need to search for your)
  6. Save your modified file
  7. Load the modified file to another database or in place of the old one (you should have a backup of it. If you use another database do not forget to change the value in the config.php file to fit the new one)
  8. Open the phpmyadmin operations page for the database and set to utf8_unicode the general database charset
All should return to run fine.
It is not a complete solution for all situations but it can give you the way to proceed and solve your problem about Illegal mix of collations.