VBA Exception Slipping Through Handler - vba

Question

I have inherited a hideous Excel VBA application, written by a guy who apparently didn't like functions and comments. Opening the source code is like staring into an abyss of madness, with 9 levels of hell indentation awaiting to trap the unwary.
First, the setup.
In the process of debugging an intermittent issue, I have identified a particular line in the primary function as its location. Since the exception is not easy for me to fix, I gave this line, and only this line, an error handler that displays a custom message.
' Lots of stuff cut out
On Error GoTo TechReleaseBuildError
lb_Err1 = BuildDirectories(gj_TechBld.mt_TechRlsOutDir)
On Error GoTo 0
' Lots of stuff cut out
Exit Sub
TechReleaseBuildError:
MsgBox "Error building tech release. Pause the synchronization software and try again."
Stop
Resume
End Sub
The Stop and Resume are only there to help debugging, since the normal error messages that pop up don't have an option to debug the error.
Within the BuildDirectories function, I have identified one line that was causing the error that was being kicked up to primary function. I have placed error handlers in this function as well.
' Lots of stuff cut out
Exit Function
TEST:
Stop
Resume
SynchroRetry:
Dim CurrentError As ErrObject
CurrentError = Information.err
SynchroRetryCounter = SynchroRetryCounter + 1
Debug.Print "Synchro Error, retrying #" + SynchroRetryCounter
Stop
If SynchroRetryCounter > 5 Then
Stop
Information.err.Raise CurrentError.Number, CurrentError.Source, CurrentError.Description, CurrentError.HelpFile, CurrentError.HelpContext
Else
Application.Wait Now + #12:00:03 AM#
Resume
End If
End Function
At the very beginning of BuildDirectories I have placed an On Error GoTo TEST statement as a catch-all error handler so I can identify what lines they are coming from, and also used the SynchroRetry handler for the one line that I already know causes an issue, which I immediately reset back to the TEST handler. The SynchroRetry handler just waits for 3 seconds and retries, failing after the 5th retry.
' For some reason, this line (and only this line so far) causes problems when synchronization software is running.
' The error handler waits for a few seconds then tries again a few times.
Dim SynchroRetryCounter As Integer
SynchroRetryCounter = 0
On Error GoTo SynchroRetry
lj_FSO.CopyFile Source:=lt_RPOFilePath & lt_RPOFileName, Destination:=lt_VinRposDir & "\" & lt_RPOFileName, OverWriteFiles:=True ' Trouble line
On Error GoTo TEST
I have verified with Find that these are the only 3 On Error statements in the function (the only ones in the module, even). The top-level function also has no On Errors other than the two shown.
In brief summary, the top-level function has an error handler on only one line, and the function it encloses also has two error handlers inside it, one for one of its known troublesome lines and a general one that should be encompassing the entire function.
The problem is that some error is occurring that is causing my "Error building tech release." message to display, but does not seem to be triggering the TEST or SynchroRetry error handlers. I cannot imagine how this is possible. I'm relatively new to VBA's monstrosity of an error handling model, but I don't believe I did anything wrong. Did I miss some subtlety here? How is an exception able to bypass my handlers and bubble up the stack like this? I do not believe the assignment or passing of the function value could cause the problem, since their just a Boolean and String value. The problem is also intermittent, and only appears when we have file synchronization software active on the directory this program is copying files to.

Answer 1

So a couple hours after I posted this, I managed to figure it out.
The reason that the Debug button wasn't on the error boxes is because in Options the Error Trapping was set to "Break on Unhandled Error". Changing it to "Break in Class Module" brought the button back.
The reason the exceptions were bypassing my error handlers is because they were happening in my SynchroRetry error handler. In particular, I had to change the first few lines from this:
Dim CurrentError As ErrObject
CurrentError = Information.err
SynchroRetryCounter = SynchroRetryCounter + 1
Debug.Print "Synchro Error, retrying #" + SynchroRetryCounter
to this:
Dim CurrentError As New ErrObject
Set CurrentError = Information.err
SynchroRetryCounter = SynchroRetryCounter + 1
Debug.Print "Synchro Error, retrying #" + CStr(SynchroRetryCounter)
Note the additions of New, Set, and CStr.
Problem solved.