Hi Stephen, Thank ypu for the extra files and information. I've been investigating your code further and I understand from your comments that the problem lies in the 'InletKernel_RegisterAllEvents2.vi', is this correct? However I still need the .dll, executable or control which supplies 'InletKernelInterfaceLib.IInletSystem2' to continue my investigations as I do not have that on my installation and it appears to be part of you application. With that file I can follow the callbacks events through and hopefully find where the problem lies. Best Regards,
Chris M Applications Engineer National Instruments (UK)