Wix does not support google adsense yet. they just add the Adsense App on there app store, But when you connect your site to your adsense google adsense show this EROE:
"Our crawler was unable to access your page to determine its content and display relevant ads. When our crawler can’t access the content, often we won’t show ads resulting in lower revenue and coverage. At other times, we’ll show ads that are irrelevant resulting in lower CTR. Follow the links in the ‘How to fix.’ column to correct these errors and improve AdSense performance."
wix support team does not support at all, They just copy and paste the foolish answered.
I'm sorry that you are experience a confusing error message on the Google side. Let me see if I can explain.
I want to assure you that what you are reading on Google's Adsense site will in no way affect your Adsense Ads or results standing within Google.
Wix has added a robots.txt to noflashhtml and backhtml files that are contained in all Wix sites, to prevent Google from crawling the noflashhtml and backhtml links inside Wix sites. These files are necessary parts of Wix websites, but we are eliminating Google's ability to see them.
The robots.txt error you are seeing has no negative effect on Google crawling and indexing your website.
At Wix, you can be sure that we are doing everything we can to make sure that your site is crawled by Google and that your Adsense app will work correctly.