Hi,
In general vCO can have administration group and all its member users will have unlimited access( view, execute, edit ant etc) . All other users that are part of non-admin groups won't be able to access vCO unless they have at least VIEW rights on the ROOT object. So to give rights for the this non-admin group, a user from the administration group should first log in vCO and configure at least VIEW rights for the root object (object at the top of the inventory) for the specific non-admin group. VIEW rights will allow the users of the non-admin group only to log and browse the objects.
So, in your case I guess you need to log in the vCO with a user from the administration group and set VIEW and EXECUTE rights of the top/root object for the group which 'MyUserName' is member of.
Regards,
Radostin