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Error 1406 could not write value to key - download problem Adobe Reader 8.0

I have computer with OS: Windows XP Home + SP2 and all updates installed
After removing Adobe Reader 7.09 and disabling the firewall, anti-spyware and anti-virus software, I installed Adobe Reader 8. Like so many others I got the error message: Error 1406 could not write value to key:
HKLM\SOFTWARE\Classes\.pdf\PersistentHandler, and
HKLM\SOFTWARE\Classes\CLSID\{B801CA65-A1FC-11D0-85AD-444553540000}\PersistentHandler

Although not an expert I started to follow the recommendations given in different communications of this forum related to the registry errors caused by AR 8 in the above two keys.
I am the only user and owner of the computer but I noticed that several group or user names have some kind of ownership accept my own name as administrator.
I have succeeded to modify the ownership of the key: HKLM\SOFTWARE\Classes\.pdf\PersistentHandler,

However I have not been able to change the ownership of the key HKLM\SOFTWARE\Classes\CLSID\{B801CA65-A1FC-11D0-85AD-444553540000}\PersistentHandler . This key does not accept the change or upon closing the tab it jumps back to the former ownership.

Can somebody tell me what I did wrong or give some hints own I should go about this problem?

As mentioned in the forum I also found some references to AR7 under some keys in the registry. I made corrections.

Under key: HKLM\SOFTWARE\Classes\CLSID\{B801CA65-A1FC-11D0-85AD-444553540000}\PersistentHandler I noticed that under ProdID reference was made to AcroExch.document7. I changed this into AcroExch.document8. Is this correct or should I change it back to the document7 denomination?

Where can I still find Adobe Reader 7.09 in case I have to go back? At the Adobe web side I cannot find it anymore.

Hope somebody can help me. Thank you
Rien