Acrobat 9 on windows vista 32 bit home premium - repeated reactivation

Every time I open a pdf after installing acrobat 9 pro., I get a message stating that my
system has changed and that the software needs to be activated again. Attempts to
reactivate online result in a reply message that the software is activated on more than
one system, which it is not. I then activate by telephone, successfully, but the very
next time I open a pdf, I get the same message that the system has changed. I have been
stuck in this infinite loop for about a month. I have contacted adobe four times by
telephone regarding this matter, to no avail. At one point, the adobe rep. researched a
little further and told me I would receive an email within 48 hours with guidance on how
to solve this problem. The email never came and the next telephone call to adobe was as
useless as the rest. Grateful to hear from others who have had similar problems, and perhaps a solution. Much more of this, and I would advise others to seek other document alternatives before upgrading to acrobat 9.