problem downloading 10.7 from app store

hi community!

i have a almost virgin installation of 10.6 on late macbook 2007 (only MS office 2011, chrome and dropbox installed), approx 30GB free space, 4GB Ram.

10.7 was already up and running fine before the reinstallation of 10.6.

I wanted to download/upgrade to 10.7, but download from app store fails ("there was a problem"), i tried multiple times, also with restart. i also tried a .dmg install file of 10.7, "there was a problem installing".

Has anyone any idea?

(I need 10.7 for my software but I dont have the money for new mac...)

would appreciate your feedback, apple specialists of the world!

cheers!!