How to check if a doc is open...

Hello all:

I have a question... :?:

I need to know if a document is being opened at this moment, so, if another user try to open it, can show a message like: "This document is in use, try later...".

I have a table named "Documents". Each record is a physical document in my pc:

This is the situation:

* I open a document (word,excel... any other) from within Nav.
* Just before open it, mark as TRUE a boolean field named "In Use".
* If another user try to open the same doc, if "In Use" is true, the message "This doc. is being used...." appears.
* When the first user close the application, Navision change the field "In Use" to FALSE.

This is my code:

VARS
WSHShell Automation 'Windows Script Host Object Model'.WshShell
AppExe Text
WinStyle Variant
bWaitOnReturn Boolean

CODE
IF RecDoc.InUse = TRUE THEN
  ERROR('The document %1 is being used...',RecDoc.Name);


IF ISCLEAR(WSHShell) THEN 
  CREATE(WSHShell);
AppExe := '"C:\MyExeProgram.exe " "' + RecDoc.Name + "';
WinStyle := 1;
bWaitOnReturn := TRUE;

RecDoc.InUse := TRUE;
RecDoc.MODIFY;

WSHShell.Run(AppExe,WinStyle,bWaitOnReturn);

RecDoc.InUse := FALSE;
RecDoc.MODIFY;

This code runs ok but there is a problem. Because bWaitOnReturn is TRUE, Navision hopes the application ends, and then, the user cannot work in any other form.

Thanks.