unable to install to Macintosh HD after SSD install

I installed an SSD in place of my old HD and placed my HD in place of the optical drive. My MacBook had been running slow and I wanted to improve its performance.

There is improvement alright but now I'm unable to unstall any apps on my HD which I planned to use as storage for audio files, plugins, libraries etc.

What to do?

I've ran a permissions check and checked user access settings but to no avail.