>>>Dragan,
>>>
>>>I've had something like this when using a Treeview.
>>>My "solution" was to make an object reference just before the failing line, then use that full object reference in the (previously) failing line.
>>>oTemp = Thisform.XXXX.yyyy
>>>abc = oTemp.GetKey(.....)
>>
>>We do think alike... that's the first thing I tried. That's how I actually discovered it had gone null.
>
>Dragan,
>
>Just a thought - could it be a VFP reserved word. It looks like it, thus erratic behavior...

It's not mentioned anywhere in the help - word Param is used in a few places, but not in the language itself, rather as a part of an example.

Somehow I get the feeling that the collection is not a VFP base class, it's taken from somewhere else (a C++ library) and it has a few things where it behaves somewhat differently - and then also a couple of glitches.
Since in my case re-adding the collection from scratch doesn't hurt (at least as long as it doesn't happen once I've set the parameters), I'm OK with the current workaround.