[RESOLVED] Uncaught SyntaxError: Unexpected token U in JSON at position 0 - The Grid

Help please

I am trying to edit the Grid skin – but there is an error on the skin builder page – which I am having issues with.
this is causing the page to crash / no responsive to clicks – therefore cannot edit The Grid skins.

Error is :

admin.php?page=the_grid_skins_overview:1 Uncaught SyntaxError: Unexpected token u in JSON at position 0
    at JSON.parse (<anonymous>)
    at Function.n.parseJSON (jquery.js:4)
    at admin-ajax.js:874
    at admin-ajax.js:1965

I have turned of all hosting caching – cleared all local browser cache
I also deleted The Grid Plugin (after exporting my grids for backup) then reisntalled from X admin page.

Still error occurs
I checked with wordfence to check for any errors / editing of plugin files – didn’t find any

Is there anything else you can suggest I look at before I look for plugin conflict ?

Many thanks

Mark

[RESOLVED] Uncaught SyntaxError: Unexpected token U in JSON at position 0 – The Grid