Satinder singh

I solved same for my blog by editing Robots.txt file.

Set my robots.txt as
Method 1:

User-agent: *
Disallow: /wp-admin/
Disallow: /wp-includes/
allow: /wp-content/plugins/
allow: /wp-content/themes/

Method 2:

#Googlebot
User-agent: Googlebot
Allow: *.css
Allow: *.js

# Other bot spider
User-agent: *
Disallow: /wp-admin/
Disallow: /wp-includes/

Using Method 2 issue will be fixed only for GoogleBot. If in future Bing / Yahoo or any other bot also throws same warning then you apply method 1

Detailed Article: How to fix “Googlebot cannot access CSS and JS files”

I solved same for my blog by editing Robots.txt file.
Check: Fix : Googlebot cannot access CSS and JS files