Vista - USB Drive required for every application installation

Hello,

Upgrading from XP to Vista, I have saved my personal files on an USB drive.
Unfortunately, I have left it connected during the upgrade process. The
upgrade was successful, no major issues except that every time I want to
install a new application, I get an error message telling me that my USB
drive is missing. I connect it, and the installation works fine as well as
the USB drive.
Does anyone know how I could remove this USB drive from the Vista "memory"
to avoid this problem.

Thank you in advance for your help.

Regards,

Arnaud.