populate table from multiple other table - null error

I'm using 10.02.00.04 working with enterprise database.

I'm trying to pre-populate a table with data from 2 other tables.  modifying gr005 my rule works fine as long as all the fields I'm pulling from have a value.  Otherwise I get this:

When I try to edit my sql query to use ISNULL I get

sSql = "Select [LABSAMPLES].GintRecID, [LABSAMPLES].gINTProjectID, [LABSAMPLES].PointID, [LABSAMPLES].Depth, [LABSAMPLES].SampleNO, [LABSAMPLES].SampleDepths, [LABSAMPLES].Visuals, " & _
    "[FIELDLITHOLOGY].GintRecID, [FIELDLITHOLOGY].gINTProjectID, [FIELDLITHOLOGY].PointID, [FIELDLITHOLOGY].Depth, " & _
    "IsNull([FIELDLITHOLOGY].Color, 'x' )" & _
    " From [LABSAMPLES] Left Join [FIELDLITHOLOGY] On [LABSAMPLES].gINTProjectID=[FIELDLITHOLOGY].gINTProjectID And [LABSAMPLES].PointID=[FIELDLITHOLOGY].PointID And [LABSAMPLES].depth=[FIELDLITHOLOGY].depth" & _
      " Where [" & s_samp_table & "]." & gs_PointID & " = '" & _
                     gINTRules.GridData.ForeignKeyValues(gs_PointID) & "'" & _
         " and [" & s_samp_table & "].gINTProjectID = " & CStr(gINTRules.EnterpriseCurrPrjID) & _
         " Order By [" & s_samp_table & "]." & gs_Depth

the code translates into this which works fine if i run it on the sql server

Select [LABSAMPLES].GintRecID, [LABSAMPLES].gINTProjectID, [LABSAMPLES].PointID, [LABSAMPLES].Depth, [LABSAMPLES].SampleNO, [LABSAMPLES].SampleDepths, [LABSAMPLES].Visuals, [FIELDLITHOLOGY].GintRecID, [FIELDLITHOLOGY].gINTProjectID, [FIELDLITHOLOGY].PointID, [FIELDLITHOLOGY].Depth, IsNull([FIELDLITHOLOGY].Color, 'x' )

From [LABSAMPLES] Left Join [FIELDLITHOLOGY] On [LABSAMPLES].gINTProjectID=[FIELDLITHOLOGY].gINTProjectID And [LABSAMPLES].PointID=[FIELDLITHOLOGY].PointID And [LABSAMPLES].depth=[FIELDLITHOLOGY].depth

Where [LABSAMPLES].PointID = '1' and [LABSAMPLES].gINTProjectID = 2

Order By [LABSAMPLES].Depth

any help would be greatly appreciated.