I've experienced this problem several times recently. I go to a production in my development instance and click on the (+) to add a new service. A pop-up appears with the message "An error occurred with the CSP application and has been logged to system error log (^ERRORand nothing else. Examining ^ERRORS is of no help. There's a lot of gibberish there that isn't informative in the least.

I can add processes and operations just fine.

I've never had a problem changing the content-type on a response using either %CSP.Page or %CSP.REST until now. No matter where I put the line to set the content-type to "application/json", it stubbornly emits a content-type of "text/html".

In OnPreHTTP: (I tried one at a time)
either
    do %response.SetHeader("content-type", "application/json") // didn't work
or
    set %response.ContentType = "text/plain" // didn't work

The same lines in OnProcessInput() didn't change the output content-type, either.