Registry permissions prevent the changes again.
Follow the instructions below. If anything is unclear, just ask first.
Click Start typ regedit in the searchbox and press enter.
Allow the program to run.
"Registry-editor" will open. On the leftside browse to the key
HKEY_CLASSES_ROOT\CLSID\{B54F3743-5B07-11cf-A4B0-00AA004A55E8}\InprocServer32
Rightclick on it and select Permissions.
A new window opens, click the button Advanced.
A new window opens, select tab Owner.
Put a checkmark at Replace owner on subcontainers and objects
Select Administrators (...) then click Apply and OK.
In the list "Group or user names" select Administrators (...).
Next, put a checkmark to allow "Full Control" and click OK.
Rightclick the registry-key again and select Add - String Value.
If you see a new key added in the right pane, name it ThreadingModel
Were you able to add this key ?