In the racle 10g Web page OEM, the account entered by host credentials is available

In Oracle 10 Gb web edition OEM, an account with operating system permissions is required for database recovery, shutdown, and other operations: Host
Credential. If you enter any administrator account, an error is returned.

Solution:
Choose Security Settings> Local Policies> User permission assignment> Add the Administrator account to be used as the host credential in Batch Job logon.

The OCP book describes the problem as follows:
In Windows, the operating system account you are using must have been granted the "log As A Batch
Job permission. Note that, by default
The Administrator account does not have this permission! See how to grant this permission in the Windows document, and note that there are changes between different versions. Whether in
In Windows or UNIX, the operating system account you use must be a member of the Oracle software owner group.