Purchase Receipt - The resource you are looking for is not available

I am trying to make a purchase receipt from a purchase order and suddenly after the page is loaded I get this message:

But I don’t get any error log.

Could you please give me some suggestions about how to trace this error or what I need to check further?
Someone already got the same issue?

ERPNext: v11.1.42 (master)

Frappe Framework: v11.1.37 (master)

Yes odd but by design a popup message and not traceback for a defective .py file (that failed to compile to a pyc?)

Have you custom code, if so where?

These 2 cases refer to code syntax issues:

“error in your python syntax, which meant the method couldn’t be found”

“keep your whitelisted method out of the class declaration and indent it towards the left”

The same problem in this case. Is exist another reason of 404 error?

                method: <path.to.method>,
                args: {
                    "items": form.get_values(),
                    "doctype": cur_frm['doctype'],
                    "docname": cur_frm['docname']

This part of code should call this python code:

def send_to_maileva(items, doctype, docname):
    items = json.loads(items)
    #another code

All path written correct (i tried execute it by bench execute <path.to.method> and all correctly executed. Which reason could be there?

To rebuild recompile the code may work -

bench build

frappe@erpnext:~/frappe-bench$ find . -name '*.pyc' | xargs rm -f

@clarkej Thank you for your help, but it isn’t helped(