Hi @rups
Done the test, and I think this is just a refresh problem of the code editor.
My guess is that the error you’re reporting is a Semantic Error one, correct?
These errors are reported by the static code analyzer, which is triggered each time the code is modified, or the editor is opened.
But as soon as your definition files are configured correctly (and this is the case now), if you open again the code editor, these errors should disappear, as the static code analyzer will be refreshed at this time.
Another option to refresh is a right-click on the project, then Run C/C++ code analysis
But please be careful that these errors are not yet compilation errors (reported as C/C++ Problem in the Problems view). Compilation errors will be reported when you explicitly build the project (with the hammer or run button in the toolbar). And typically, with this code, you’ll see that you have compilation errors 
Anyway, I’m logging the point, and we’ll check if we can avoid this refresh behavior in DS.
Finally, by the way, please avoid posting topics on both forums (cf http://forum.mangoh.io/t/error-while-accessing-le-dataconnection-api-methods/424/4)
Legato forum is the good place for generic software oriented questions. MangOH forum is more dedicated to MangOH hardware/software specific questions.
Thanks!