Chrome theme building issue: cannot decode image

[divi...@gmail.com]

Hello

I am in the process of creating a theme for chrome, however i encountered an issue, and i seem to be too stupid to see the error of my ways. 

Facts: 

- I can use my theme by installing "unpacked version" via extension manager = No issues 
- I can install my unpacked theme using chrome app development toolkit       = No issues


But when I upload the theme in zip file to chrome store, i cant install it anymore. -> Package is invalid. Details: 'Could not decode image: 'bg.png''.

Heres my manifest: 

{ 
  "description": "some description",
   "manifest_version": 2,
   "name": "some name",
   "icons": { "128": "icon128.png" },
   
   "theme": {
         "colors": {
         "bookmark_text": [ 0, 0, 0 ],
         "frame": [ 135, 180, 78 ],
         "ntp_background": [ 255, 255, 255 ],
         "ntp_link": [ 0, 0, 0 ],
         "ntp_link_underline": [ 0, 0, 0 ],
         "ntp_text": [ 0, 0, 0 ],
         "tab_background_text": [ 0, 0, 0 ],
         "tab_text": [ 0, 0, 0 ],
         "toolbar": [ 179, 217, 133, 0.6 ]
      },
      "images": {
         "theme_frame": "img/theme_frame.png",
         "theme_ntp_background": "img/bg.png",
         "theme_tab_background": "img/theme_tab_background.png",
         "theme_toolbar": "img/theme_toolbar.png"
      },
      "properties": {
         "ntp_background_alignment": "top",
         "ntp_background_repeat": "no-repeat"
      }
   },
   "version": "1.0.9"
}

Thing is. . . before packing up everything works like a charm. All the files are in their respective locations.
I have tried different file format for the ntpbackground, i have tried jpg, jpeg, gif, png etc etc . . .
I have tried different compression levels from no compression at all to outright disgusting . . .
I have tried to move file elsewhere and change its path in manifest. . . .

NOTHING seems to work and I have not a slightest clue anymore what could be the problem.