SaveAs goes to exception if Find/Replace dialog is open

[rain]

Hi,

I am developling word automation.
Save a doc first, and open Find/Replace dialog. Focus on doc and change
something. Press Ctrl+S for Save and immediately focus on Find/Replace
dialog. Code aDoc.SaveAs(FileName, FileFormat, typemissing,
typemissing......) goes to exception said "The SaveAs method or property is
not available because the find or replace dialog box is open".
Why? And how could I solve this problem?

Thanks in advance.