Upload image cannot be displayed

My client used FCKfinder to upload a jpeg image. Serveral times the thumbnail of uploaded image can only be displayed as a question-mark image in FCKfinder image browser. On the other times thethumbnail of the uploaded image can be displyed normally in the image browser, but when the image was added to the web page, the web page cannot display the image. When tried to open the image in browser, the browser reported that the image contains error. When download the image to my local PC, it can be displayed normally. Is the issue related to FCKfinder? thx