I repeatedly see this error in my logs and found to be occuring while creating a page.
*ERROR* [0:0:0:0:0:0:0:1  GET /etc/designs/ewcmsc.thumb.60.60.png HTTP/1.1] org.apache.jsp.libs.foundation.components.primary.cq.Page.thumb_png_jsp resource has no content. path=/etc/designs/ewcmsc.thumb.60.60.png referrer=null
After initial tracking this message is coming from /libs/foundation/components/primary/cq/Page/thumb.png.jsp where it includes /libs/foundation/components/primary/cq/Page/proxy.jsp
proxy.jsp has the error situation handled but I could not get the reason behind the thumbnail error and this error.