I was having this problem recently, trying to upgrade SV11 to built 521.
I am running Win 7 Pro and solved it using the following website.
You have to remove the locks on the folders once that is done it works
To find the right folders to un-lock wait till the installation fails and read the directory beneath the error, you may have to do this a few times to un-lock them all.
If no message is given as to the folders that were the locked, then go to
look for something like this.
(use CTRL+F in Notepad and enter ERROR and then did find next)
” SetupWorkerThread: INSTALLMESSAGE_ERROR Error writing to file: C:\ProgramData\Sony\Vegas Movie Studio HD Platinum\10.0\Vegas profiles update.ini. Verify that you have access to that directory.”
Go to the directory stated and unlock.
|1603||The file  is being held in use by the following process: Name: , Id: , Window Title: ‘’.||A system restart may be required because the file being updated is also currently in use. Users may be given the opportunity to avoid some system restarts by using the FilesInUse Dialog or the MsiRMFilesInUse Dialog. For more information, see System Reboots and Logging of Reboot Requests.|