If you are using LINUX/Windows the hostname credentials should be the same user who has installed the oracle database software, if Windows the user you are using need to be member of the ORA_DBA group and have Local Security privilege ‘Log on as a batch job’.
What you need to do is go to:
Local security policy —>
Local policies —>
User rights assignments
In the list to your right, look for ‘Log on as a batch job’, double click and add the same OS local user you using to access OEM web to the group.
I hope this tips will help you solve your problem
Francisco Munoz Alvarez