SQL converting data problem (nvarchar to numeric)

Hi
Having a problem converting data.  This is the query I'm using that's failing with Msg 8114 level 16 state 5: "Error converting data type nvarchar to numeric":


SELECT
      --c.WorkOrderNumber as 'DBR Workorder Leg',
      LEFT(c.WorkOrderNumber,LEN(c.WorkOrderNumber)-7) as 'COSS Workorder',
      --d.CloseDate,
      --a.ScheduledEndOperation,
      a.ActualEndOperation as 'Machine Leg End',
        --forgweight.datavalue as 'Forge Weight',
   --   machweight.datavalue as 'Machine Weight',
     
      --cast(ISNULL(forgweight.DataValue,0) as decimal(10,3)) - cast(ISNULL(machweight.DataValue,0) as decimal(10,3)) as PoundsRemoved,
      --e.ForgeWeight,
      --e.MachineWeight,  
      --forgweight.datavalue as 'Forge Weight',
      machweight.datavalue as 'Machine Weight',
      forgweight.datavalue as 'Forge Weight',  
        ISNUMERIC(ISNULL(forgweight.DataValue,0)) as 'FORGEVALUETEST',
        ISNUMERIC(ISNULL(machweight.DataValue,0)) as 'MACHVALUETEST',
     CAST(ISNULL(forgweight.datavalue,0) as numeric(15,5)) as 'Forge Weight',
     CAST(ISNULL(machweight.datavalue,0) as numeric(15,5)) as 'Machine Weight',
  --    case when CAST(ISNULL(forgweight.datavalue,0) as decimal(10,3)) > '1' then CAST(ISNULL(forgweight.datavalue,0) as decimal(10,3)) - CAST(ISNULL(machweight.datavalue,0) as decimal(10,3))
            --else 0 end as PoundsRemoved,
      CONVERT(CHAR(3), a.ActualEndOperation, 0) + ' ' + CAST(DATEPART(YEAR,a.ActualEndOperation) as varchar) as MonthYear
     -- case when e.ForgeWeight<e.MachineWeight then '0' else e.forgeweight-e.machineweight end as PoundsRemoved
      --e.ForgeWeight-e.MachineWeight as Pounds
      --(CONVERT(INT,REPLACE(left(e.ForgeWeight, len(e.ForgeWeight) - charindex('.', reverse(e.ForgeWeight))),',','')) -
      --CONVERT(INT,REPLACE(left(e.MachineWeight, len(e.MachineWeight) - charindex('.', reverse(e.MachineWeight))),',',''))) as PoundsRemoved
      --e.ForgeWeight - e.MachineWeight as PoundsRemoved,
FROM [houdev\coss].DBROld.dbo.qryRopeItems a
            JOIN [houdev\coss].DBROld.dbo.tblWorkorders c
                  on a.WorkOrderID = c.WorkOrderID
            JOIN [houdev\coss].DBROld.dbo.tblWorkorderStatus d
                  on c.WorkOrderID = d.WorkOrderID
            --LEFT OUTER JOIN atf.dbo.COSS_vw_WorkOrders_Dimensions e
            --      on LEFT(c.WorkOrderNumber,LEN(c.WorkOrderNumber)-7) = e.WorkOrderNumber
                  --on RIGHT(RTRIM(c.WorkOrderNumber),11) = RIGHT(RTRIM(e.WorkOrderNumber),11)
            left outer join forg.dbo.coss_workorder e
            on LEFT(c.WorkOrderNumber,LEN(c.WorkOrderNumber)-7) = RTRIM(e.UsrDfnId)
            LEFT OUTER JOIN forg.dbo.COSS_CustomAttributeValue forgweight
            on e.ident = forgweight.OwnerIdent and forgweight.AttribName = 'Forge Weight'
            LEFT OUTER JOIN forg.dbo.COSS_CustomAttributeValue machweight
            on e.ident = machweight.OwnerIdent and machweight.AttribName = 'Machine Weight'
            
WHERE --a.OperationDescription = 'MACHINE SHOP COMPLETE' --and--
            c.WorkOrderNumber like '%MACH' and
            a.ResourceID = '2'
      and (DATEADD(D, 0, DATEDIFF(D, 0, a.ActualEndOperation))  between '2014-06-01' and '2015-06-10')
      --group by LEFT(c.WorkOrderNumber,LEN(c.WorkOrderNumber)-7), a.actualendoperation, forgweight.DataValue, machweight.DataValue
      


I can comment out: CAST(ISNULL(forgweight.datavalue,0) as numeric(15,5)) as 'Forge Weight',
and if I do, the query runs without any issues.

I've tried running this to find out whether there's a non-numeric value in there, but I get no results:

SELECT
      --c.WorkOrderNumber as 'DBR Workorder Leg',
      LEFT(c.WorkOrderNumber,LEN(c.WorkOrderNumber)-7) as 'COSS Workorder',
      --d.CloseDate,
      --a.ScheduledEndOperation,
      a.ActualEndOperation as 'Machine Leg End',
        --forgweight.datavalue as 'Forge Weight',
   --   machweight.datavalue as 'Machine Weight',
     
      --cast(ISNULL(forgweight.DataValue,0) as decimal(10,3)) - cast(ISNULL(machweight.DataValue,0) as decimal(10,3)) as PoundsRemoved,
      --e.ForgeWeight,
      --e.MachineWeight,  
      --forgweight.datavalue as 'Forge Weight',
      machweight.datavalue as 'Machine Weight',
      forgweight.datavalue as 'Forge Weight',  
        ISNUMERIC(ISNULL(forgweight.DataValue,0)) as 'FORGEVALUETEST',
        ISNUMERIC(ISNULL(machweight.DataValue,0)) as 'MACHVALUETEST',
       --CAST(ISNULL(forgweight.datavalue,0) as numeric(15,5)) as 'Forge Weight',
     CAST(ISNULL(machweight.datavalue,0) as numeric(15,5)) as 'Machine Weight',
  --    case when CAST(ISNULL(forgweight.datavalue,0) as decimal(10,3)) > '1' then CAST(ISNULL(forgweight.datavalue,0) as decimal(10,3)) - CAST(ISNULL(machweight.datavalue,0) as decimal(10,3))
            --else 0 end as PoundsRemoved,
      CONVERT(CHAR(3), a.ActualEndOperation, 0) + ' ' + CAST(DATEPART(YEAR,a.ActualEndOperation) as varchar) as MonthYear
     -- case when e.ForgeWeight<e.MachineWeight then '0' else e.forgeweight-e.machineweight end as PoundsRemoved
      --e.ForgeWeight-e.MachineWeight as Pounds
      --(CONVERT(INT,REPLACE(left(e.ForgeWeight, len(e.ForgeWeight) - charindex('.', reverse(e.ForgeWeight))),',','')) -
      --CONVERT(INT,REPLACE(left(e.MachineWeight, len(e.MachineWeight) - charindex('.', reverse(e.MachineWeight))),',',''))) as PoundsRemoved
      --e.ForgeWeight - e.MachineWeight as PoundsRemoved,
FROM [houdev\coss].DBROld.dbo.qryRopeItems a
            JOIN [houdev\coss].DBROld.dbo.tblWorkorders c
                  on a.WorkOrderID = c.WorkOrderID
            JOIN [houdev\coss].DBROld.dbo.tblWorkorderStatus d
                  on c.WorkOrderID = d.WorkOrderID
            --LEFT OUTER JOIN atf.dbo.COSS_vw_WorkOrders_Dimensions e
            --      on LEFT(c.WorkOrderNumber,LEN(c.WorkOrderNumber)-7) = e.WorkOrderNumber
                  --on RIGHT(RTRIM(c.WorkOrderNumber),11) = RIGHT(RTRIM(e.WorkOrderNumber),11)
            left outer join forg.dbo.coss_workorder e
            on LEFT(c.WorkOrderNumber,LEN(c.WorkOrderNumber)-7) = RTRIM(e.UsrDfnId)
            LEFT OUTER JOIN forg.dbo.COSS_CustomAttributeValue forgweight
            on e.ident = forgweight.OwnerIdent and forgweight.AttribName = 'Forge Weight'
            LEFT OUTER JOIN forg.dbo.COSS_CustomAttributeValue machweight
            on e.ident = machweight.OwnerIdent and machweight.AttribName = 'Machine Weight'
            
WHERE --a.OperationDescription = 'MACHINE SHOP COMPLETE' --and--
            c.WorkOrderNumber like '%MACH' and
            a.ResourceID = '2'
      and (DATEADD(D, 0, DATEDIFF(D, 0, a.ActualEndOperation))  between '2014-06-01' and '2015-06-10')
      --group by LEFT(c.WorkOrderNumber,LEN(c.WorkOrderNumber)-7), a.actualendoperation, forgweight.DataValue, machweight.DataValue


Out of ideas.  Please let me know what you think