Hey saska987,
No problem. Would you mind showing me your Static Mesh settings? Particularly the UV channels you are using for your mesh as well as the build settings?
Also, you still might want to try messing around with the Lightmass settings that you had already mentioned. Try setting your Smoothness value to something like 0.6.
One of our team members has comprised a great bit of information on how to troubleshoot Lightmap issues where you might also find a way to fix your issue.
Lighting Troubleshooting Guide
Let me know if you are still not able to get it to light correctly, or if one of the suggestions within the Guide worked for you.
Cheers,