Visio diagram in word 2003

[JohnM]

I have Visio for Enterprise Architectct (11.4301.6360) and Word 2003
(11.5604.6360). I start a word document, go to insert->object->visio , and
insert and edit a visio document. I now move the cursor to some other
location on the page and add text. At some point, the visio drawing changes
into a bitmap, and I can no longer edit it. If I select "object" from the
context menu, the dialog appears "This object is corrupt or no longer
available".

I can insert a new vision drawing in the same document, but again after some
event, the drawing turns into a bitmap.

Any ideas? Thanks