Frustrating Visual Studio Crashes When Adding Script Step

I have two similar packages that are both experiencing this issue.

I need to add a script step to generate an incrementing id for the packages.

Once I add the script step, and then save the package, next time I open the package I get a "Microsoft Visual Studio has encountered a problem and needs to close" error which kills off Visual Studio.

The error signature is:
EventType: clr20r3
P1: devenv.exe
P2: 8.0.50727.762
P3: 45716759
P4: microsoft.sqlserver.txscript
P5: 9.0.242.0
P6: 443f5ab8
P7: 67
P8: d
P9: bbp0yyyc15o2dbouwcacz2m0bodqkotn

If I move the error window to one side, delete the whole Script step, and save the Package, then I can reopen the package again without the error occurring.

Here is the actual code in my script step (in case its of any assistance...)
(I have retyped it from a printout, so it may not be 100%. DOCID is supposed to increment from 1. DREF1 is a system-unique id, that takes up from where the last batch left off, and is a string prefixed by "MP")




Code Snippet

Imports System
Imports System.Data
Imports System.math
Imports Microsoft.SqlServer.Dts.Pipeline.Wrapper
Imports Microsoft.SqlServer.Dta.Runtime.Wrapper

Public Class ScriptMain

Inherits UserComponent
Dim ndx as Int32 = 0

Public Overrides Sub Input0_ProcessInputRow(Byval Row as Input0Buffer)

'
' Add your code here
'
Dim dref as String

ndx = ndx + 1
Row.DOCID = ndx

dref = "MP" + Ctype(ndx + Variables.MPIDOrig, String)
Row.DREF1 = dref
End Sub

Protected Overrides Sub finalize()

Variables.MPID = ndx + Variables.MPIDOrig
MyBase.Finalize()
End Sub
End Class