Hello,
If you are running Windows 2008 R2 try to start the omniinet service on client using a domain account and , on the Cell Manager
use the command line :
omniinetpasswd -add User@Domain Password
( user: account name / domain : domain in which account had been created / password: user's one )
you can verify using omniinetpasswd -list
Try to install client again using this account.
Hope it will help.