June 20, 2013 
Readers have reported problems running this file on Windows in FileMaker 11. The problem is that with a Web Viewer on Windows, Internet Explorer, the underlying technology behind the Web Viewer on Windows doesn’t like raw JSON files returned from MailChimp. There are some other solutions for FM 11, but it is fairly simple to fix this problem using FileMaker 12 by replacing the Web Viewer parsing routines with the new “Insert from URL’ script step.
Here is the FM12 Mailchimp Demo file.
Insert from URL in action
Here is a sample script employing the Insert from URL script step. Instead of setting a Web Viewer and having a loop to wait for html source text to be returned, this is a single step operation. The peculiarity of this step is that it needs to insert the value into a text field (no Set Variable option) and that text field must be on the layout for the script to run properly. This got me a few times, I had the script setting a global field and neglected to add it to the layout.
MailChimp Integration with FileMaker Pro – Part 1 of 4
MailChimp Integration with FileMaker Pro – Part 2 of 4
FileMaker MailChimp Integration – Part 3 of 4
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Brilliantly helpful. Thank you very much.
Have you done any work on this with the new OAuth2 methods yet??
Both the 1.2 and 1.3 \API methods are now deprecated and it might make sense to jump straight in with the new ones.