Why do I get these weird Artifacts in Lightmap Bake when switching from 3.5.7 to 4.1.2 (after Re-Baking) NOT Blotches! But Vertical and Banding Artifacts

Hello Community, I'm experiencing weird issues with Lightmapping with Beast on my newly installed Unity 4.1.2f1 TRIAL Version. When I lightmap it with Unity 3.5.7f6 I get a very nice satisfying Lightmap Bake, couldn't be happier. BUT when I Bake the very same scene again in my Trial Unity 4.1.2f1 I get very nasty Vertical Artifacts and Banding etc. And stuff looks like it is not dithered or something. (Please see the pictures attached) I'm not talking about blotches or anything like that. No matter at what Resolution or how many Final Gather Rays I use, the artifacts don't go away. (I went as high as 5000 FG and 512 Resolution) On the Unity 3.5.7f6 install I get a great Bake even at low resolution of 50 an FG at 1000 or lower. Having the Lighmaps uncompressed doesn't solve it either. It's driving me nuts... If you guys need more info please let me know. (I have attached some images) Any help would be appreciated! Thank you very much in advance.