Sudden error with posts

Hey,

Something wierd really happened.Almost all the following chars from my posts transformed into ? : “space”,” ‘ “, ” ” ” and ” ; “.I don’t know why this happened but my blog worked perfectly untill today when i installed wp-cache2( i heard is very good for optimizing speed) and i optimized my tables from phpmyadmin ( i backed up the database first).After i saw this error,i restored the database and the same problem. Now,i can edit evert single post and replace the ? with the good char,but why did it do that and how can i avoid it in the future.

Tnx in advance