Access to Mozilla version control systems is handled centrally via LDAP and uses SSH public keys. Changes to LDAP accounts, and SSH key issues, are handled by the MOC.
Mozilla VCS (e.g. hg, svn) accounts may be disabled due to inactivity if no commits are made in a six month time frame. Activity on one VCS is not linked to any other VCS (i.e. commits to SVN will not prevent an inactivity lock on Hg).
To have access re-enabled, please file a bug with the MOC, and include the push error message and email address used on the account.