take a look at the comments in standalone/configuration/mgmt-users.properties.
Which AS version are you using? By default the versions released with that realm didn't have the security switched on by default so it would suggest someone has switche on security for the version you are running.
I have got the same problem after fetching the latest changes from github. I was asked for a login and password for accessing to management console.
I needed to uncomment the example definition of credential in mgmt-users.properties and then I could use admin/admin for login or I think when you don't need the security check for accessing the console you can delete attribute 'security-realm="ManagementRealm"' in standalone.xml under the <management-interfaces> tag for appropriate interface.
You would have had a similar problem not the same problem, once security is enabled by default the realm name is 'ManagementRealm' but the original poster is having a problem related to the realm 'PropertiesMgmtSecurityRealm' which suggests someone has already manually enabled security on their installation.
Yes,I put my question again because I'm configuring Jboss is the Jboss web-as-7 and I need help whit this problem :-)