So, I researche the forum and tried all the proposed solutions, which are:
Clear cache and cookies
Check the image parameters (jpg, 900kB)
Try to upload from a different page (tried from Find Job, there is no upload option)
And still, aI am getting the same error : Sorry, something went wrong. We were unable to upload your image.
Please help me, what else can I do?
I fixed it. The problem was that my picture was of 4500px height. I did not know that the higher border of resolution existed, because only there parameters are specified on the upoad page: "250x250 Min size/ 5 MB Max".
So I just cropped it and it worked.