Does REST API "Update Landing Page Template Content by Id" still work?

I tried to make use of the PHP sample snippet on Update Landing Page Template Content by Id » Marketo Developers​ with substituting my REST API URL, client_id, client_secret, and a simple template file. It simply produces bool(false) as a result.

When I used a slightly different equivelent, I found that my REST call results in... object(stdClass)#3 (3) { ["requestId"]=> string(16) "e714#153c7bf644f" ["success"]=> bool(false) ["errors"]=> array(1) { [0]=> object(stdClass)#4 (2) { ["code"]=> string(3) "611" ["message"]=> string(12) "System error" } } }

What's up with the mysterious error code 611?

// Victor