I have a service that accesses a VB6 COM component on a timer event. On
64-bit windows (running in 32-bit "mode") the process fails if it is run in
a secondary thread but works fine when run on the main thread. This
behavior cannot be re-produced in 32-bit environment.

Any help would be greatly appreciated.

The error is:

System.InvalidCastException: Unable to cast COM object of type 'blah.type'
to interface type 'blah.interfacetype'. This operation failed because the
QueryInterface call on the COM component for the interface with IID
'{[guid....]]}' failed due to the following error: Error loading type
library/DLL. (Exception frm HRESULT: 0x80029C4A (TYPE_E_CANTLOADLIBRARY)).

The exact code from the same components runs fine in 64-bit environment
(again running in 32-bit mode) if it is not run on a secondary thread.

I'm not using a primary interop assembly and nothing is running from the GAC
except framework stuff.

thanks,
-chris

I should mention: All code is C# targeting x86 cpu using framework 2.0

i have a "fairly" simple example that demonstrates the problem.

-chris

"Chris Yager" <chris.yager (AT) gldsolutions (DOT) com.invalid> wrote

I'd considered that but it behaves well in 32-bit windows.

thanks for the response,
-chris

"Mattias Sjögren" <mattias.dont.want.spam (AT) mvps (DOT) org> wrote

Hi Chris,

the error message indicates that the typelib cannot be loaded - can you
load it manually using LoadRegTypeLib (on 64-bit windows) or do you get
the same error?

--Johannes

Chris Yager wrote:

--
Johannes Passing - http://int3.de/

Thanks to all for the help.
The problem was the apartment state.

I spawned an additional thread off the timer's thread and set the apartment
state to "STA" and everything works as expected.

Thanks again,
-chris

"Mattias Sjögren" <mattias.dont.want.spam (AT) mvps (DOT) org> wrote