Today I needed to log into a Oracle instance using OEM to look at some users and roles. I found that when attempting to log into the instance with the sys username and password and as sysdba I was getting insuffcient privledges. Well I immediatley logged into the host machine and I was able to login via sqlplus with the same credentials. I tested OEM against other Databases and had no issues. Then I remembered that this instance had been built not to long ago. I went and looked and I did not see the password file. Once I moved that from another host to this one, I was in. Just make sure you have that password file.