Can not upload screentshots

We wanted to update the game info on APP Center, it requires 3 screenshot for APP on facebook, however, the place to upload the screenshot didn't pop up the “+” pic like the other place to upload, it always show "no defaul image uploaded", we clicked it, and nothing happened. It had been worked well in the early stages, and becomed bad after we added the multiplied language. We have tried many browsers and gotten the same result. Please help us to fix this.

Li Qimiao
Asked about 2 months ago