Javascript Error during uploading using Uploads field

Hi,

I have upgraded to the latest version of joomla (3.8.10) and Cobalt (8.762) and add an Uploads field to my type. Everything is on default mode and when I add a file it starts to uploading it and stop it and shows following error in my console window:

VM1613:1 Uncaught SyntaxError: Unexpected token < at JSON.decode (mootools-core.js?feb48b13b994b4d890d40477862bc3e4:172) at Object. (MooUpload.js:1153) at Object. (mootools-core.js?feb48b13b994b4d890d40477862bc3e4:42) at Array.forEach () at Function.forEach (mootools-core.js?feb48b13b994b4d890d40477862bc3e4:5) at Array.each (mootools-core.js?feb48b13b994b4d890d40477862bc3e4:9) at Object.fireEvent (mootools-core.js?feb48b13b994b4d890d40477862bc3e4:42) at Object.e.extend.$owner (mootools-core.js?feb48b13b994b4d890d40477862bc3e4:38) at Object.onSuccess (mootools-core.js?feb48b13b994b4d890d40477862bc3e4:160) at Object.e.extend.$owner (mootools-core.js?feb48b13b994b4d890d40477862bc3e4:38)