I have seen some similar posts, but none seems to be my case exactly. I have WordPress and Piwik set up on a separate subdomains (cms.mydomain.com and analytics.mydomain.com). I have WordPress publishing static pages to the root (www.mydomain.com).
I set Piwik up with a new user that has "view" access to my site (it is pointing at http://www.mydomain.com rather than WordPress). In the WP-Piwik configuration I have added "analytics.mydomain.com" and the token for the new user. I am receiving the error message: "Please check URL and auth token. You need at least view access to one site."
When I click on the "Support" link, it says that cURL is available and allow_url_fopen is enable. When I run the test script it us successful. When I take the URLs our of the test result and paste them in Chrome with the correct token, they return the same XML messages. When I click on site configuration details, they are successfully and correctly returned except that "ID" is a dash (Site ID is correct). I have tried resetting WP_Piwik settings once to no avail.
Any ideas on what I am missing?