Recently upgraded an IMSS installation from 7.0 to 7.1 and as part of the upgrade the setup utility wants to upgrade SQL to SQL Server Personal Edition 2005 (if you're using the old MSDE version)

During the SQL Server upgrade process, the upgrade halted with a notice about UpGrade Advisor Returned Error -1.  You have to essentially cancel the SQL upgrade which then cancels the IMSS upgrade.

To work around the issue, do this:

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Typically under C:Program FilesMicrosoft SQL Server90Setup BootstrapBPA (or insert your path here) there is a folder called BPA and under the child folder called "bin" there is a file called bpaclient.dll. 

Create a new folder under the C:Program FilesMicrosoft SQL Server90Setup BootstrapBPA folder called BPACLIENT and move the bpaclient.dll file into that folder from the bin folder, reboot the system, and rerun your upgrade...it should work!