Xp_fixeddrives

I have a monitoring site setup that looks at different aspects of the database and the health, and the latest addition is checking drive space.

I know you can use master..xp_fixeddrives to return all the drives and space that is available. But when I run this through an OpenQuery it errors out:

"select * from openquery (test_server,'exec master..xp_fixeddrives')"

"Cannot process the object "exec master..xp_fixeddrives". The OLE DB provider "SQLNCLI" for linked server "test_server" indicates that either the object has no columns or the current user does not have permissions on that object."

Any suggestions??

Thanks.