I've spent 3-weeks browsing for the answer to this problem, and although
there were a few promising threads already open here, none quite duplicate
the problem I have.
After buying a new PC ready-installed with Vista Home Premium, everything
worked fine for a few weeks, I could install programmes from CD or the
Internet without any problem when signed-on with a User account set as
'Administrator' rather than 'General User'.
Then for no apparent reason (I hadn't fiddled with any settings) I became
unable to install programmes from any source, CD or internet. It appears that
the PC now thinks that all User Accounts have 'General User' rights,
including those set as 'Administrator'.
The exact error message I get reads "You do not have sufficient priveleges
to complete this installation for all users of the machine. Log in as an
Administrator and then retry this installation".
I have read the help solutions on this site on the
page, which suggest right-clicking on installation icons and then clicking
'Run as administrator', but this doesn't make any difference. I've also tried
downloading installation files to the PC rather than running from the
internet, but that makes no difference either.