Native Def:
//Get the size and type for the specified attribute ID.//
KPDCStatus KPDCGetAttributeInfo(KPDCOpaqueRef inRef, KPDCAttributeID
inAttrID, KPDCDataTypes *outAttrType, KPDCUInt32 *outAttrSize);

My wrap:
Declare Auto Function KGetAttributeInfo Lib "DCSPro4SLR.dll" Alias
"KPDCGetAttributeInfo" (ByVal inRef As IntPtr, ByVal inAttrID As Integer,
ByRef outAttrType As KPDCDataTypes, ByRef outAttrSize As Integer) As Integer

Native Def:
//Get the value of the specified attribute ID. If the attribute is the
KPDCPropValueID of a property, then the value of the property will be
retrieved from the camera.//
KPDCStatus KPDCGetAttributeValue(KPDCOpaqueRef inRef, KPDCAttributeID
inAttrID, KPDCUInt32 *inOutAttrSize,

My wrap:
Declare Auto Function KGetAttributeValue Lib "DCSPro4SLR.dll" Alias
"KPDCGetAttributeValue" (ByVal inRef As IntPtr, ByVal inAttrID As Integer,
ByRef inOutAttrSize As Integer, ByVal outAttrValue As IntPtr) As Integer

Native Def:
//Allocate a property iterator for camera properties.//
KPDCStatus KPDCAllocPropertyIterator ( KPDCCameraRef inCameraRef,
KPDCPropertyIterRef *outRef);

My Wrap:
Declare Auto Function KAllocPropertyIterator Lib "DCSPro4SLR.dll" Alias
"KPDCAllocPropertyIterator" (ByVal inCameraRef As IntPtr, ByRef outRef As
IntPtr) As Integer

Native Code:
//Return a reference to the first item that has the string specified by
inName and the value of its name attribute. The iterator points to the found
item. A subsequent call to KPDCIteratorNext returns the item following the
found item in the list.//
KPDCStatus KPDCIteratorFind(KPDCIteratorRef inIteratorRef, const char
*inName, KPDCOpaqueRef *outFoundItemRef);

My Wrap:
Declare Auto Function KIteratorFind Lib "DCSPro4SLR.dll" Alias
"KPDCIteratorFind" (ByVal inIteratorRef As IntPtr, ByVal inName As
System.Text.StringBuilder, ByRef outFoundItemRef As IntPtr) As Integer

Native Code:
//Return a reference to the next enumerated item. After creating a new
iterator or calling KPDCIteratorReset, this function returns the first item.
If there are no more items, outNextItemRef will not be valid.//
KPDCStatus KPDCIteratorNext(KPDCIteratorRef inIteratorRef, KPDCOpaqueRef
*outNextItemRef);

My Wrap:
Declare Auto Function KIteratorNext Lib "DCSPro4SLR.dll" Alias
"KPDCIteratorNext" (ByVal inIteratorRef As IntPtr, ByRef outNextItemRef As
IntPtr) As Integer

Native Code:
//Reset the iterator to point to the beginning of the list.//
KPDCStatus KPDCIteratorReset(KPDCIteratorRef inIteratorRef);

My Wrap:
Declare Auto Function KIteratorReset Lib "DCSPro4SLR.dll" Alias
"KPDCIteratorReset" (ByVal inIteratorRef As IntPtr) As Integer

Thank you for your patience. I noticed this article on your site:
http://support.microsoft.com/?kbid=309327

It breakes unmanaged resources into 2 types, handles to operating system
objects, and non operating system objects.

What would constitute an operating system object?

Sorry I keep doing this, but as I type things out, I'm working it out in my
head. You should also know that in the C++ demo code, they have a typedef
section that looks like this:
TypeDefs in demo C++ code:
typedef void*           KPDCOpaqueRef;
typedef KPDCOpaqueRef   KPDCLibMgrRef;
typedef KPDCOpaqueRef   KPDCIteratorRef;  
typedef KPDCIteratorRef  KPDCCameraIterRef;
typedef KPDCOpaqueRef   KPDCCameraRef;
typedef KPDCIteratorRef  KPDCPropertyIterRef;
typedef KPDCOpaqueRef   KPDCPropertyRef;
typedef KPDCIteratorRef  KPDCDirectoryIterRef;
typedef KPDCOpaqueRef   KPDCDirItemRef;
typedef KPDCOpaqueRef   KPDCIORef;
typedef KPDCOpaqueRef   KPDCImageRef;

Most of the function declarations use these. After looking through the
article I mentioned in the previous reply, I am wondering, should I use
HandleRef instead of IntPtrs? And how do I know when to use what?

I really think that this is something with garbage collection, because it is
happening after the managed function (which calls to the unmanaged function)
is called.