If you are attempting to execute STSADM commands, and are receiving the ominous “Object reference not set to an instance of an object” error, make sure that the user account that are using to execute STSADM has permissions to the SQL database.  I ran into an issue today where the domain account had permissions to the WFE but not to the SQL server, and whereas I could work in Central Admin, and perform other Farm Administrator duties, STSADM commands were failing with the above error.  Once my account was added to the local Administrators group of the SQL server the STSADM commands executed without fail.