can not install lion

Hi there,

i am having problems with installing lion: i was running 10.6.8. and tryed to install the lion upgrade but it gives me an error (can not install mac os x on this disk until the installation process was about 50 %). The disk utility give me no errors (before upgrading), permissions were also ok.

then i tried to make a "clean installation" with the dvd - it also doesn't work --> the same error (can't install mac os x)

any ideas what i can do to get the new lion installed on my MBP 13, middle 2010 ?

thx, Alex