I am using the Postie plugin for a couple of WordPress sites. But in one site, it literally took my hours and lot of coffee to fix it. Note I was using the mail server as mail.mysitename.com (Read mysitename as my domain)
After upgrading Shop.wayanad.co.in from Opencart 126.96.36.199 to 188.8.131.52, I found lot of errors/bugs which needs minor changes in config files, vqmod re-install etc. and was fixed.
But an error which stalled me from editing/updating orders killed my time a lot. It was “syntax error JSON.parse unexpected end of data at line 1 column 1 of the JSON data”
After googling and wandering opencart forums, i found the post http://www.viethemes.com/how-to-fix-error-syntaxerror-unexpected-end-of-input-ok-when-editing-order-in-opencart-2/ which helped me to fix this error.