The other day I ran across an error with the massProperties and submit it to GoEngineer and got a SR Number 1-1366886371

and a SPR # 521659 ,  the sent me some code for a work around,

I haved never used CreateMassProperty before so I did some testing

and found  this

download bug.zip and extract files then  open Assem1

check the mass of Assem1 then check the Mass of Assem2

then check mass of part1

open Assem2

and run code
--code --
Sub test()
     Debug.Print ("----------start------------------------------")
    Dim swApp                   As SldWorks.SldWorks
    Dim swModeldoc              As SldWorks.ModelDoc2   
    Set swApp = CreateObject("SldWorks.Application")
    Set swModeldoc = swApp.ActiveDoc 
    Dim vMassProp               As Variant

    vMassProp = swModeldoc.GetMassProperties
    Mass = vMassProp(5) * 2.20462262
    Debug.Print ("GetMassProperties Mass:  " & Mass)
    Dim MassProp                As SldWorks.MassProperty

    Set MassProp = swModeldoc.Extension.CreateMassProperty
    Mass = MassProp.Mass * 2.20462262
    Debug.Print ("CreateMassProperty Mass: " & Mass)

    Debug.Print ("----------end--------------------------------")      
End Sub

----------start------------------------------
GetMassProperties Mass: 13.2058611510285
CreateMassProperty Mass: 0.164532147827838
----------end--------------------------------

then unsuppress part2 re-run code

----------start------------------------------
GetMassProperties Mass:  13.2058611510285
CreateMassProperty Mass: 13.2058611510285
----------end--------------------------------

the resurpress part2 then run re-code

----------start------------------------------
GetMassProperties Mass:  0.164532147827838
CreateMassProperty Mass: 0.164532147827838
----------end--------------------------------

the CreateMassProperty is aways right

CreateMassProperty is also better to get the properties from

CreateMassProperty Mass = MassProp.Mass * 2.20462262  [ this is  SldWorks.MassProperty]

GetMassProperties   Mass = vMassProp(5) * 2.20462262  [ this is a Object]

I will only use CreateMassProperty for now on