After uninstalling SQL Server 2008 R2 Standard and reinstalling, the following error occurs.
"Rule 'Consistency validation for SQL Server registry keys' failed". The SQL Server registry keys from a prior installation cannot be modified. To continue, see SQL Server Setup documentation about how to fix registry keys.
After checking the Install Logs I found that there was a missing file. 'FixSqlRegistryKey_x86'.
This is interesting as I was performing the x64 install and the directory was \x64.
As a temporary workaround I just extracted the missing 'FixSqlRegistryKey_x86.exe' file into the \x64 directory from the \x86 directory and re-ran setup.
I did not have to adjust any registry keys as the help indicated.