After searching this forum and Google, I didn't find what I was looking for. So I now following the advice to start a new topic for this (at least for me) unknown error.
The problem is coming/part off/generated (perhaps by me) from an http request node.
To explain it more: I have a device with a webpage.image1
It has two switches: sw_0 and sw_1.
If in the browser I type:image2 I can put sw_1 on.
Or: image2a to put sw_1 off.
So far so good but when I now try to get info from this page with a http request node, I get this error, HPE_INVALID_CONSTANT under the node and in the debug window it shows "Error: Parse Error".
I guess I am doing something completely wrong.

[{"id":"8da0b852.8c87e8","type":"inject","z":"7b226f34.d363","name":"","topic":"","payload":"","payloadType":"date","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":160,"y":140,"wires":[["714af8ec.a24cd"]]},{"id":"1995a2a9.f4a055","type":"debug","z":"7b226f34.d363","name":"","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","x":570,"y":140,"wires":[]},{"id":"714af8ec.a24cd","type":"http request","z":"7b226f34.d363","name":"","method":"POST","ret":"txt","url":"","tls":"","x":350,"y":140,"wires":[["1995a2a9.f4a055"]]}]

I did this ones before with a webpage that showed some values of temperature and humidity but that seems not to work with this one.
Any ideas how to solve this? Thanks for reading.



Generally that means there is an issue with the html being returned by the website.
When you look at the page with a browser, what page is returned. Does the browser console indicate any errors?