Format the C: drive and install a fresh copy of Windows.

Just asking the obvious, did you do the workstation install with "right click, run as administrator" and did you run the regacc with "right click, run as administrator" just because it works with the admin user...

We did all the step above you mentioned. The issue is we cannot assign the user as an admin user or we cannot share the admin password. It is managed by group policy. 

"This user is not having the same issue on another machine and other user are not having the same issue on this error machine".  Install a fresh copy of Windows.

I have had this before;

- it was when I had installed the shared directories in a separate folder on the server (Sage300 & Sage300SharedData).

- when I then installed on a Win 7 workstation, it did not update the registry properly.

- it used Sage300 as the shared data

- So I changed the registry shared data entry to Sage300SharedData and the workstation worked after that.

I am not sure if this could be your problem - no harm in checking !!!