I have to invoke a C++ function from VBA/Excel that does a callback. I've
isolated the problem I'm having in the code below.

In the C++ (complied & linked to a DLL) I have:

long __stdcall tryCB3(long n, long (*cbFunc)(long m))
{
long r;
r = cbFunc(n); // call back
return r;
}

In the VBA I have:

Private Declare Function tryCB3 Lib "SparkExUtilsDll.dll" _
(ByVal n As Long, ByVal theFunct As Any) As Long

Public Function theCBFunc3(ByVal m As Long) As Long
Debug.Print "In theCBFunc3"
theCBFunc3 = m * m
End Function

Public Function tryCBDrv3()
Dim n As Long
Dim q As Long
n = 2
q = tryCB3(2, AddressOf theCBFunc3)
Debug.Print "n= " & CStr(n)
Debug.Print "q= " & CStr(q)

End Function

When I step through tryCB3Drv it calls tryCB3, and then steps through
theCBFunc3, all working as expected, but then crashes with a C++
error dialog saying the ESP was not preserved through a function call etc.

Note that the it works without crashing if the callback function
has no arguments, so it must be some problem with the way VBA is setting
up the argument to theCBFunc3, vs. the way it's declared in C++.

Any ideas?

TIA

Ed