pb with modal windows of embedded Word instance

[Bidon]

I use an embedded word instance in my application (Word is
in activated in place in a frame of my application).
This application manipulates a thread which frequently
post messages to my application to manipulate the embedded
word instance.

It works fine except when I opens some modal windows of
Word (in my frame). The modal windows start to blink (I
think it's the messages posted by my thread )

I want to avoid to manipulate word when a modal is shown
but I don't know how to do. Moreover I noticed that the
method to get the application interface doesn't work
(hangs in fact) when a modal is shown.

Any help would be welcome.
Thx a lot