Hubert Nguyen,
 

If the CuteEditor security policy file, you find the following setting:
 
<security name="OverWriteExistingUploadedFile">false</security>
 
If the file is already available when uploading, CuteEditor won't allow the file is uploaded.
 
You can set it to true if you want to disable this feature.

 

Please note that you can programmatically set this property.