Hi,
When you interrupt the secondary dialog box "Select Reference File" with cancel or the [X] button, you'll get the following events triggered (and a sample arguments that they have) -
:VLR-documentLockModeWillChange . (#<VLA-OBJECT IAcadDocument 00000017039a28c8> 4 2 4 "#XATTACH")
:VLR-documentLockModeChanged . (#<VLA-OBJECT IAcadDocument 00000017039a28c8> 4 2 2 "#XATTACH")
However if you choose a (dwg) file and get into the third dialog box "Attach External Reference", and cancel or [X]-it it... then you'll get -
.. some events ...
:VLR-dwgFileOpened . (#<VLA-OBJECT IAcadDatabase 000000170166a768> "C:\\<Path>\\Test.dwg")
.. some events ...
:VLR-documentLockModeWillChange . (#<VLA-OBJECT IAcadDocument 00000017039a28c8> 4 2 4 "#XATTACH")
:VLR-documentLockModeChanged . (#<VLA-OBJECT IAcadDocument 00000017039a28c8> 4 2 2 "#XATTACH")
Finally if you are able to attach the dwg, then you'll get -
... bunch of object opened, appended, modified events...
:VLR-xrefSubcommandAttachItem . (4 nil)
.. some more events...
:VLR-commandEnded . ("XATTACH")
:VLR-documentLockModeWillChange . (#<VLA-OBJECT IAcadDocument 00000017039a28c8> 4 1 4 "#XATTACH")
:VLR-documentLockModeChanged . (#<VLA-OBJECT IAcadDocument 00000017039a28c8> 4 1 2 "#XATTACH")
Good Luck!