EndDrag Access violation

I've converted a module from Delphi 1 code to Delphi 3 and now get an error
"Access violation at address 004213CD in module 'Login.Exe'.  Read of
address FFFFFFFF."  Tracing through the code reveals that the crash occurs
immediately after an EndDrag method call.  The Delphi 1 code doesn't crash
after the EndDrag.  The object is a TOutline type and I've even replaced one
16-bit TOutline object to the Win32 TTreeView object in an attempt to fix
the bug, but with the same crash on both the TOutline and TTreeView objects.

Does anyone know what could be the cause?  Has the Delphi 3 EndDrag behavior
changed in some way?

I've posted the 'Access violation' error earlier with a response that the
message refers to an object instantiation/destruction problem, but I've
checked the code and haven't found that to be the case.