The versionlock list format is NOT compatible with default 'rpm -qa' output.
The locked packages and their versions need to be listed in ENVRA format:
EPOCH:NAME-VERSION-RELEASE.ARCH

That format can be easily generated with repoquery (also part of yum-utils)
with --envra option. If for example you want to lock what's currently on
the system you could use 
   
  repoquery --quiet --envra --pkgnarrow=installed -a 

If using repoquery isn't an option for whatever reason, the following
queryformat will extract ENVRA format from rpm:

  rpm -qa --qf "%|epoch?{%{epoch}}:{0}|:%{name}-%{version}-%{release}.%{arch}\n"