drupal 6.x - login problem with *Clean Urls turn ON*

dear Sirs,

i used drupal for few sites, now i intalled fresh new drupal 6.1 for my new site,
now I have big problem:

after TURN ON Clean Urls I can not log on as Admin from frontpage (www. mysite. com)! It redirects me to /node/?destination=node with error: "You don't have permission to access /node/ on this server."

i can log on only from *non-fronpage* (www. mysite. com/admin)

i tried to seach for solutions at drupal.org but can not find it.

Please give me a hint.

Thank you very much.