Loss of admin rights - partially

A strange loss of rights. I am admin on the computer and can install programs after entering my password. Updating installations fail, however. Mac OS upgrades pass.

I've discovered that it is when the new install has to overwrite an older installation and delete the old version. Initially the pw is accepted and it proceeds to write files. After this it fails with a message quite simply 'installation failed - try again'.
If I first delete the old version (admin pw there too) then install it works.
Permissions repair has not solved the problem the only corrections there were to some Java stuff.

Any ideas how to correct this?

Tel.