Adobe Air Apps for OS X: Unable to build a valid certificate chain for the signer. // Code Signing on OS X 10.10 Yosemite

Hi,

I created several OS X Apps using Adobe Air. That worked quite well before. Now I have do update my OS X Apps - therefore I also needed update my certificates. [ I'm using Flash CC 2014 on OS X Yosemite 10.10 ]. But whatever I do it doesn’t work anymore. I always get this Message saying:

Unable to build a valid certificate chain for the signer.

I googled a lot and the only "guide" I found is this post (from April 2013) about code singing - http://scottgaertner.com/code_signing/

I’m not used to deal with this kind of stuff (CA etc.) - so it's quite confusing to me.

Would anybody please be so kind and tell me what I have to do?

Is there any instruction from Adobe? (I didn't find one yet) 

A step by step instruction for absolute dummies would be great!

Best regards and thank you in advance

Jan