What is it's file size?
From what I can see of the current settings, the max dimensions allowed for a Profile Photo is set to 100x100 pixels (so you're within that setting), but the maximum allowed file size is 64KB.
You'll see those limits if you go to your User Control Panel (User CP choice at the top of each page) and select the "Edit Profile Picture" choice. This is what you'll see on that page:
Quote:
"Note: The maximum size of your custom image is 100 by 100 pixels or 64.0 KB (whichever is smaller)"
So, if the file size of your photo exceeds 64KB (unlikely given an image with dimensions that small if it's jpeg), it will probably fail to upload, even if the dimensions in pixels are within limits.
I'd check the file size and if it's larger than allowed, go to the editor you used to save the image and use a different JPEG quality setting (most editors will have a JPEG quality slider you can use when using their File>Save As menu choice), until the file size is within the allowed limits.
Just to make sure, you are talking about your "Profile" photo, not your Avatar (something different), right?
If it's within the allowed limits, see if you can attach it to a reply in this post and I'll see if I can duplicate the problem. It's just a standard jpeg file, right?