Looks like that chomikuj.pl URL is password protected but the prembox.com API doesn't have the possibility to even ask for a password.
Instead it returns this:
Code:
{"success":false,"error":"invalidUrl","errorDescr":[]}
Contact the prembox.com support and ask them to return the correct errormessage in case of a wrong given password.
This is not a JD issue!
-psp-
EDIT
I've also forwarded this to the prembox.com support.