About certificates


I have some problems with the certificates. I requested many times the certificates from the certification bureau but some of them I even couldn’t place in the keychain access and others were after I had placed them there with the red colored message “the certificate is xxxxxxxx unreliable”. Can somebody explain me why and how to fix this problem?
I know that possibly it’s not related to the app development, but to others it definitely does not relate to others.
Note: Now I have deleted most of these certificates. And also, a few minutes later I found that the certificate I couldn’t place in the keychain access is there but with the same red colored message.