If I recall correctly, the "Check in use" command is not reliable.
Have a look in the Wisescript library at Dragonsoft as they have some process monitoring wisescripts which will do the job for you much more reliably. Alternatively, use WMI

What is WMI? and how do i use it? I've heard the term before but not familiar with it.

WMI stands for Windows Management Instrumentation and is a very powerful tool for finding out about the hardware and processes on a windows PC. You basically code in vbscript.
If you want to see how many functions are available in WMI, grab a copy of WMIExplorer (google for it) and have a look on your current system.

So for example, if you want to see if calc.exe is running, this is how you would do it in a simple example:

Dim Wmi, Wql, Processes
 IsRunning = False
 Set Wmi = GetObject("winmgmts:")
 'Check if the Calc.exe Running
 Wql = "select * from Win32_Process " & " where name='" & "Calc.exe" & "'"
 Set Processes = wmi.execquery(wql)
 If Processes.Count > 0 Then
  MsgBox "Calc is running Please Close Calc.exe"
 End If

Of course, once you are coding in vbscript, you can use the session.property method to pass information to and from an MSI via public properties
eg:  session.property("PROPERTYNAME") = Processes.count  would pass the value in Processes.count from the example above, into a public property called PROPERTYNAME.

Try googling on "WMI" and see how much information is literally at your fingertips !!