I had the same problem, and the way I worked around it is probably not the best but it is working now.
It involves creating a linked server and using dynamic sql - not the best, but if anyone can suggest something better, please comment/answer.
declare @sql nvarchar(max)
DECLARE @DB_SPACE TABLE (
[DatabaseName] NVARCHAR(128) NOT NULL,
[FILEID] [smallint] NOT NULL,
[FILE_SIZE_MB] INT NOT NULL DEFAULT (0),
[SPACE_USED_MB] INT NULL DEFAULT (0),
[FREE_SPACE_MB] INT NULL DEFAULT (0),
[LOGICALNAME] SYSNAME NOT NULL,
[DRIVE] NCHAR(1) NOT NULL,
[FILENAME] NVARCHAR(260) NOT NULL,
[FILE_TYPE] NVARCHAR(260) NOT NULL,
[THE_AUTOGROWTH_IN_KB] INT NOT NULL DEFAULT(0)
,filegroup VARCHAR(128)
,maxsize VARCHAR(25)
PRIMARY KEY CLUSTERED ([DatabaseName] ,[FILEID] )
)  
SELECT @SQL ='SELECT [DatabaseName],
        [FILEID],
        [FILE_SIZE_MB],
        [SPACE_USED_MB],
        [FREE_SPACE_MB],
        [LOGICALNAME],
        [DRIVE],
        [FILENAME],
        [FILE_TYPE],
        [THE_AUTOGROWTH_IN_KB]
        ,filegroup
        ,maxsize FROM OPENQUERY('+ QUOTENAME('THE_MONITOR') + ','''+ ' EXEC MASTER.DBO.monitoring_database_details '  +''')'
exec sp_executesql @sql
      INSERT INTO @DB_SPACE(
                            [DatabaseName],
                            [FILEID],
                            [FILE_SIZE_MB],
                            [SPACE_USED_MB],
                            [FREE_SPACE_MB],
                            [LOGICALNAME],
                            [DRIVE],
                            [FILENAME],
                            [FILE_TYPE],
                            THE_AUTOGROWTH_IN_KB,
                            [filegroup],
                            maxsize
                          )
      EXEC SP_EXECUTESQL @SQL
This is working for me now.
I can guarantee the number of columns and type of columns returned by the stored procedure are the same as in this table, simply because I return the same table from the stored procedure.