Forum ?© instead of é after upgrade
 

Our server has been upgraded to : Apache 2.4, Php 5.4.9 (Win 64) and Mysql 5.6.
(downgrade is no option) ..

Now we got a special character issue.
All the é characters becomes a ?© ..
ë characters are turned into questionmarks.

All the typed text after a special character is gone and not shown on the forum.
We tried several options.. One of them was to put a @ in class_core.php after shutdown = (we found somewhere on the internet).

We hope to get some solutions here.. Because we have users with a é in there name and they must use ?© instead.