The problem was that all my web applications ran normally on localhost, but on server the Greek characters (or any other no-english characters) displayed with problems.
So, I needed to remove BOM from hundreds view files of Yii from a lot of Yii projects manually. Netbeans has an option to keep files Encoding in utf-8 but not utf-8 without BOM.
My previous solution was the converting in utf-8 without BOM encoding one by one file on notepad++ consuming a lot of my time!
Many servers has not this issue but for other servers this is important. So, after of two hours searching I found a fast way to do that by commands.
(If you have windows, install cygwin first)
1) Open a shell command, go into your root folder that contains the project
2) Run this command
grep -rl $'\xEF\xBB\xBF' /home/rootfolder/Yii_project > file_with_boms.txt
3) Now, Run this one
while read l; do sed -i '1 s/^\xef\xbb\xbf//' $l; done < file_with_boms.txt
Thats it! The BOM will be removed from all files that contained it. Now you can upload your project on your server.
Note: Because I didn't use this way many times and I don't know if it works properly for all cases and files, make first a backup of your project! :)