OK thanks - just to double check are you fully re-indexed and fully synced (bitcoin wise)?  It looks like it from the screenshot, but bitcoin will throw a 500 if it can't find the transaction or block we're searching for.

The next library build will have some additional information provided when bitcoin returns internal server errors.

For an immediate fix on another topic, J.R. pointed me to a bug with empty history - was fixed in my smart property experimental branch but still buggy in master, so have committed that as an urgent fix.  If you get an exception because it's a fresh wallet or you've never done any Mastercoin transactions, please pull the download again for the fix.