I keep getting this message when I try to upload my photo Invalid JSON String.
Make sure that your photo size is about 150 x 150 pixels. and te format be PNG or JPG.
Also make sure that you're selecting the image icon and not the mutlimedia icon. Please see below image.
I am having the same problem for creating my profile. I have the correct size but it is still saying invalid JSON string. Please help!
I expierenced the JSON error at the end of last semester. What I found was that I was logged into more than one Moodle site in the same browser. JSON must cache some information on the browser and when more than one moodle site is trying to write info down it gets confused.
To fix this I simply use two different browsers for different sites.
Hope this helps.