Hi radmir,

The extension validation only available when you set property "AllowedFileExtensions", so if you do not want it check the extension, just do not set this property.

 <CuteWebUI:UploadAttachments runat="server" ID="uploader1">

            <ValidateOption AllowedFileExtensions="jpg" />

 </CuteWebUI:UploadAttachments> 

Regards,

Ken