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I was working on a Windows app today, when my errors were no longer being displayed as they usually would. Instead, the debugger just jumps out of the method. The output window makes a note of the exception, but the usual popup trace does not appear.

It works in other projects, and I have put Dim i as Integer = "A" as my first line to try and raise an error, but it just exits the sub on that line.

Any ideas how I get it back?

Hannele
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baileyswalk
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3 Answers3

11

There is a bug in the interaction between the debugger and the 64-bit version of Windows 7 that strikes in the Load event. An exception is trapped and swallowed by Windows, the debugger never gets a chance to detect that it was unhandled. The only thing you'll see is a "first chance" notification in the Output window. The Load event handler will immediately terminate and your program keeps running as though nothing happened, assuming that it didn't bypass a critical piece of initialization code. This bug has been around for a long time and is well known to Microsoft, apparently it is difficult to fix.

You can work around this bug with Project + Properties, Compile tab, scroll down, Advanced Compile Options button. Change the Target CPU setting to "AnyCPU". Another way to trap it is with Debug + Exceptions, tick the Thrown checkbox on CLR Exceptions. Yet another workaround is to put initialization code in the constructor instead of OnLoad() or the Load event. You only really need Load when you need to know the actual size of the window.

This bug will only strike when you debug. It won't happen on your user's machine.

UPDATE: I expanded a great deal on this mishap in this post.

Community
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Hans Passant
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Under the Debug->Exceptions check that the Common Language Runtime exceptions are checked.

BRaul
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Has your .suo file been deleted by any chance (this is the file that stores your personal state of the solution, your settings, what is expanded / collapsed). You will only really spot this if you suddenly noticed that you had to hit "collapse all" because it had forgotten, it will recreate this when you open the solution, but will do it with default settings.

If so, hit CTRL + ALT + E and re-tick the break on exceptions tick boxes for CLR exceptions.

Fenton
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  • I just checked the Thrown box and it now breaks at the error, but in my other project Thrown is not checked and still it breaks at the error. Is there any harm in leaving this checked anyway? I think it is something to do with a UnitTest that I added today, first time I have looked at them, didnt think it would do that though. Is there a better way to re-enable this? – baileyswalk Jul 11 '11 at 16:37