Thank you for the help but there was not any new information to me.
Well, it works in VIMP 2011 with exactly the same settings so this might be a bug in VIPM 2012. I simply installed VIPM 2011 back instead so now it is working again.
After upgrading to VIPM 2012 (build 1780) i am not able to download package list or download packages anymore. I get error code 42 / HTTP error 407. It seems VIPM disregards my proxy settings? Everything has always been working for me in all prior versions...
Does anyone have any ideas?