If you are installing this update and encountering problems related to "System.IO..." errors or BPACMD.EXE execution problems or missing assembly BPAClient.dll then simply create a new folder called BAPClient in your
C:\Program Files\Microsoft SQL Server\90\Setup Bootstrap\BPA\
and copy BAPClient.dll from C:\Program Files\Microsoft SQL Server\90\Setup Bootstrap\Bin folder and paste it into newly created folder BPAClient.
Hopefully it should solve all these problems and successfully intall updates. Luckly it worked for me :)
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