Return code values in SAP CRM system are 0,4,12,16 and 24...!! Is this same for R/3 System ...?

Yes in r/3 also we get 0,4,12. I never came across other 2 practically but theoretically they do exists in r/3.

In error related to security point of view...0,4,08,12...that if we check all the option i the trace than may be in program level/rfc level....we would get that i guess...but for security not needed.

There some times applicable for 08 also,we get this due to some invalid user buffer.

Based on object related to some program , dataset or rfc you get rc 12 but for other functional objects u get 08.

I had once got an RC 8 when there was a test role created in QA having the same profile name as that of the role being transported (just the profile name and not the role name) in such a case where there is a deadlock due to the profile names being the same leads to a RC 8.