Specified cast is not valid errors

Question

Hi all
Sometimes, but not always, I'm finding that the Layer.Add, Cell.GlueTo and Window.Select methods throw errors similar to:
Specified cast is not valid at System.StubHelpers.InterfaceMarshaler.ConvertToNative(Object objSrc, IntPtr itfMT, IntPtr classMT,
Int32 flags) at Microsoft.Office.Interop.Visio.IVLayer.Add(Shape SheetObject, Int16 fPresMems)
I'm using VB2010, Visio 2007 and currently testing on Windows XP 32 bit. The program is a stand-alone .exe program using Visio via .NET interop. The same program, with the same data can run several times without problem and then once this error
has been thrown, the same error will be thrown every time until the Visio file is closed and re-opened.
This VB2010 code was derived from a VB6 program which has been working fine for 2,000+ users over a period of about 15 years.
Unfortunately I've not been able to replicate these problems in a small test program which is making the debugging process rather tedious and it's another aspect of this problem which is worrying and confusing me.
The program is adding a 100 or so shapes from a stencil and gluing lines between them. I've tried playing with the settings of such properties as DeferRecalc, EventsEnabled, InhibitSelectChange, LiveDynamics, ShowChanges and UndoEnabled as I thought
Visio might be having a problem updating the screen or allocating memory to the undo manager or something. I've also tried Application.DoEvents.
I've re-written some of my code to avoid using Window.Select which I was using to select shapes to create groups. I guess I could also re-write the code to avoid using GlueTo, but I don't think I can always avoid using Layer.Add.
Any thoughts or comments would be much appreciated.
Best regards
Roger Billsdon

Answer 1

Hi Paul
Many thanks for your reply and I hope all is well with you.
I spent quite a lot of time trying to replicate the problem in a small test program created from scratch. All the offending methods (Window.Select, Layer.Add and Cell.GlueTo) worked fine in the test program, as indeed they often do in my main program.
I carefully compared all the project references and everything else I could think of in both the test and my main program. I added loops in the test program so that it added many shapes, etc in an attempt to create some stress on the Visio UI, Undo manager,
etc. Not being able to replicate the problem in a small test program is one aspect of this problem that is worrying and confusing me.
The main program is quite large (I guess about 60,000 lines of code) and contains code for many other functions. An alternative approach would be for me to take a copy of the main program and try chopping chunks out to degenerate
it into a small test program. However, at present I have a looming project deadline so I'm now putting my effort into recoding to eliminate the Window.Select, Cell.GlueTo and, where possible, Layer.Add method calls. Fortunately Visio provides alternatives
which seem to be working. For example, rather than Cell.GlueTo I'm setting the relevant cell formulae and instead of Window.Select to form group, I'm creating a shape, converting it into a group and then dropping the other shapes into this group.
Back in my VB6 programs I had some problems with select and group so I think this conversion is worthwhile, but I don't recall having had any problems with Cell.GlueTo or Layer.Add. Because I don't understand what's causing the problem I'm concerned that this
re-coding work is just fixing the symptoms without actually getting at the root cause.
In general I am finding rather more problems and performance issues with VB.NET Visio programs than I did over all the years I used VB3 and VB6 to program Visio.
Best regards
Roger