the warning tells you theres a problem with the security of the rpm package, check out this
link for a response to someone who has had a similar problem. but, as it says, it is only a warning.. and isnt the cause of the 'error' at all.
as ubertnut said, try creating the directory:
mkdir -p /usr/src/redhat/SOURCES
the -p option creates all parent directories as necessary.. although it doesnt make sense that the cause is that it cant make that directory