I found the solution and like to write down that here for the case, the someone runs into the same problem.
In my case, I downloaded the angular-google-maps extension from github, extracted that zip-file on windows an copied the file to my project. With the result, that an error occurs: Failed to instantiate module google-maps due to ...
while loading "the same" js file over http everything works fine. The point is: it's not the same file!
The solution is to take the file from the URL Link and storing local:
Maybe during downloading or extracting, the zip-file was broken. Maybe there is an character problem. Whatever.
If I open that link http://www.directiv.es/application/html/js/nlaplante/angular-google-maps/angular-google-maps.js
in an browser, I can right-click that file and open the source in an "source-code" editor and save that file on disk.
Now I can copy that new created file into my project folder like that location: js/libs/directiv.es/angular-google-maps.js
and everything works fine.....