Dreamweaver error decoding the saved files

Hi there,
Suddenly this error appeared in the middle of the project. I can’t pass this error message and also I don’t know how to solve it. I saved my project and loaded it again and the same error appeared again. Can anyone help me please to fix this one ? What is causing this ?
Thank you !

Dreamweaver
The document’s current encoding cannot correctly save all of the characters within the document. You may want to change to UTF-8 or an encoding that supports the special characters in this document.
