Impossible to install drivers

Hello, I have a Mac Book 2008 with Snow Leopard 10.6.8.

I'm trying to install 3 drivers (one for an external sound card, two for midi controllers), all from different companies (Native Instruments and Allen&Heath) but during the installation process, at the last step, it says that a problem has occurred and it is not possible to install the driver.

Any suggestions?

Thank you in advance 😉

Luca