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I developed a small application which accesses a MS access database on my computer using VB.net. I developed the program on windows xp 32 bit. At the moment I am using windows 7 64 bit and the program simply will not run. I get a null reference exception when I try to do anything to the database. I have narrowed this down i THINK to the db provider. I was using Provider=Microsoft.Jet.OLEDB.4.0; and tried using Provider=Microsoft.ACE.OLEDB.12.0;. Neither seems to work. The path to my database is 100% correct. This is the error I am getting:

Null reference exception was unhandled. Object reference not set to an instance of an object.

Like I say the program runs fine on the windows xp machine. If it helps the access database file extension is mdb.

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No DLL exist for 64 bit access to Access database files so you must go to the project properties and on the "Compile" tab go to "Advanced Compile Options" and set "Target CPU" to "x86" I hope this helps.

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I was having the exact same problem, except writing to a SQL 2008 DB. VS2008, VB.net code with framework 3.5, Windows 7 64-bit. Code runs fine on XP.

John R's answer provided the right solution: changing the project's advanced compile options to set "Target CPU" to "x86".

This problem can have more symptoms than originally described. I'll generalize them:

Accessing ACCESS isn't the only problem; it happens with SQL (at least MS SQL 2008) too.

Some of the DB calls can and do work. It's as if the calls set you up for failure, but the point of failure happens later, at a random point in your program.

The point of failure I saw was during a subroutine call. (just a normal call to a subroutine I created in VB.) Putting a try-catch block around the call wouldn't catch the error though.

Here's the strangest part: Previous to the errant subroutine call, the code had a HANDLED exception. Ironically, the exception was EXACTLY what was being thrown at the errant call. When I "tweaked" the code to avoid the prior exception, NO exception was thrown at the errant call; the VB program JUST QUIT WITH NO ERROR! It appears that whatever code is having the problem, it is reusing the last handled exception. This would mean that if your code previously had an "index out of bounds" or "divide by 0" error, this is what you'd (probably) see when the code barfs (because of no 64-bit dll.) So this problem can masquerade as a whole bunch of errors!

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Doesn't sound like a Provider error because the Jet part is fine. Make sure your Data Source path is correct. If you have it in your Projects folder on VS and are using a full path it may need to change because of how the file system is set up with Users vs Documents and Settings.

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@Nicklas look to see if you have these files. Provider=Microsoft.Jet.OLEDB.4.0 C:\WINNT\System32\Msjetoledb40.dll C:\WINNT\System32\Msjet40.dll C:\WINNT\System32\Mswstr10.dll C:\WINNT\System32\Msjter40.dll C:\WINNT\System32\Msjint40.dll
I found a good resource on this. Check out link

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