iTunes 12.3: doesn't open podcast

Hello.

I'm on a MacBook Air - 2014 model, with OS X El Capitan 10.11 installed and iTunes 12.3 installed.

(I've been having this problem since updating to iTunes 12!)

Whenever I open my iTunes and select any podcast I downloaded, I never can's hear/view the file!

A window opens telling me 'the file requires Quicktime; this application isn't supported by this version of iTunes'.

If I go into iTunes Store and select any podcast, the same happens!

Why is this happening? Also, for work related purposes, I still use QuickTime 7.6.6... before I installed it, the 'bug' already happened!

Also, I decided to clean install OS X EL Capitan... but this didn't solve the problem! Like I mentioned before, it started to happen after updating iTunes to version 12... and I was still on OS X Yosemite!

Any ideas anyone?!

Thanks in advance for any suggestions you may have!

All the best!