Decompile Your Microsoft Access Database to Fix the Bad DLL Calling
Convention Error
Provided by:
Luke Chung, FMS President and
Dan Haught, FMS Executive Vice President
Error Message and Behavior that Make No Sense
Bad DLL Calling
Convention Error
Have you seen Error 49, Bad DLL calling
convention, when running what appears to be your perfectly, well written code?
When this error occurs, it's usually after one of your procedures
finishes and
returns to its calling procedure. However, the message makes no sense
because you haven't called a DLL. Debugging and stepping through your code drives you crazy because everything is working fine, yet
the error keeps popping up.
It's driving you crazy and enough for you to throw away Access! What's going on?
Queries with VBA Functions Suddenly Fail
Similarly, do your queries that have VBA code (such as Left, Mid, or UCase)
start failing? How can something so simple all of a sudden stop working?
Compact and Repair doesn't help
This can all be very
confusing because it makes no sense. Everything looks fine. And Compact and Repair does
not help.
The initial assumption is that the database is corrupt, which is partially
true. People then resort to creating a
new database and importing their objects into it which is time consuming and
a pain. It solves
the problem, but there's a much easier way.
Possible Solutions
Fortunately, there are a few options that can resolve this problem.
Are any Library References Broken?
The first thing to check is whether the library references for your
module code are valid. From the VBA IDE, go under Tools, References to see
the list of referenced libraries and make sure none of the checked items say
"Missing" in front of them. If so, fix that and your problem should go
away. Assuming that's not the cause of the problem....
The Problem Lies with the Compile State of VBA
Unfortunately, over time, the part of your Microsoft Access database that
stores VBA module code can become bloated, and in some cases, trigger
strange errors such as Bad DLL calling
convention.
As you compile
and run code, VBA leaves behind old versions of the code that are no longer valid,
but it is not always removed from the database. Database Compact and Repair only
addresses the Jet tables in your database, and not the code. That's why it has
no impact when this error arises.
The Access /decompile command
Fortunately, Microsoft Access has a solution with the /decompile command
line option.
When Access is started with this and you open
your database, it discards all the old compilations, and leaves just your VBA source
code. You'll need to compile again to get the compiled state. After
compacting, your database may be significantly smaller.
To decompile your database, follow these steps
-
From the Windows, Start, Run command line, type: msaccess.exe /decompile
where msaccess.exe includes the complete path. For example:
C:\Program Files\Microsoft Office\Office12\MSACCESS.EXE /decompile
-
When Access opens, open the database you want to decompile (with trusted
authority for Access 2003 or later)
-
Open up any module. Compile
it via Debug, Compile.., then File, Save.
-
Go back to the database and Compact it
-
For Access 2007,
Office Button, Manage, Compact and Repair Database.
-
For Access 2003
or earlier: Tools, Database Utilities, Compact and Repair Database
The database size should be reduced and the strange
errors related to the VBA code should be gone.
The example above is for Microsoft Access 2007, but it also applies to
Microsoft Access 2003, 2002, 2000, 97 and earlier.
Create a Shortcut
To simplify doing this in the future (and you'll likely need this again), create a shortcut on your Windows desktop pointing to where your copy of Access is located:
C:\Program Files\Microsoft
Office\Office12\MSACCESS.EXE /decompile
Then, whenever your database
is acting oddly, you can easily launch the decompile version of Access to
open your database and decompile it. In a few minutes, you're back up and
running with a smaller database.
Good luck!
See Also:
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