I tested myself and Allcrypt is right - the JSON RPC interface is broken.

I tested sending getmininginfo and receive HTTP (500) Internal Server Error

Some commands work: getaccountaddress, listtransactions, getbalance

Most do not.  getpeerinfo, getinfo, getmininginfo, gethashespersec, getgenerate, many more

These commands all work from the debug console in the Windows wallet - they do *NOT* work over a http connection to the wallet.  They all return HTTP 500 Internal Server Error