hi!
i finally solved the issue!
you definitely have to install the weather gk4 file what is linked here on joomart site!
( https://www.joomlart.com/member/downloads/gavick/joomla-extensions/weather )
there exists another download of the latest weather gk4 1.8. somewhere in the web and this file is damaged!!!
on the gavik site it self, you do not get the latest version.
after installing the wheather gk4 from joomart and insert all keys and secrets, the weather modul is working well!
may this helps some other guys with this issue.....
do not download the weather gk4 on different sites, use this link and you wont get an prase error! :
https://www.joomlart.com/member/downloads/gavick/joomla-extensions/weather
greetings rob