Exchange Organization Name 2010 error

HI, When i am trying to install exchange 2010 on 2008 r2 member server, readiness check is failing at organisation prerequisites asking to modify AD with setup /prepareAD. when i ran prepareAD Eg: setup /PrepareAD /OrganizationName: xyz

i get the following error.

 Exchange organization name cannot be specified. There already exists an Exchange organization with name 'xyz'. 

i think this is because of my earlier unsuccessful attempts of installing exchange. can someone help me to get pass this. thanks

i already deleted the organisation from ADSIedit? But still i get the same error.

Thanks