Try to add features with an existing installation

Hi,
We use SQL Server 2012 sp1.
We want to install a feature that we did not install the first time.
So we run the "SQL Server Installation Center" from our server.
At the step "Setup Support Rules", we received this error:

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.

Do you have an idea how to fix that ?
regards