an error occurred while attempting to run privilaged commands!

[vdavis]

i have searched for 2 weeks all over the internet and have tried every option that i found and cannot get superuser access on my evo 4G.... when i open superuser app there is no app listed there for superuser access.... i have the gingerbread 2.16, i can boot into recovery mode with no prob.... i have tried several different superuser.zip files, the latest being 3.0.7.... can anyone help please? when i try to run rom manager it gives a message saying " an error occurred while attempting to run privilaged commands! "