Shelled Program and wait for running the third application

In my application I wait for a shelled application to
finish and
continue to work. Everything works fine but when the
shelled program is
up and user tries to open other applications (outside of
my
application) they will not be opened till the shelled
program finishes.

I tested both following methods:

'----(Method 1)----
If File.Exists(lsCasewareAppLocation) Then
Shell(lsCasewareAppLocation + " " + Chr(34) +
lsSelectedFile +
Chr(34), AppWinStyle.NormalFocus, True)
...
Else
....
End IF

'----(Method 2)----
If File.Exists(lsCasewareAppLocation) Then
Dim pInfo As New ProcessStartInfo()
pInfo.FileName = lsSelectedFile
Dim p As Process = Process.Start(pInfo)
p.WaitForInputIdle()
p.WaitForExit()
....
Else
....
End IF
------------------------

Actually this problem happens on client site when they
try to run an
accounting software and it never happens in development
area or with regular applications.

I appreciate you help on this issue.
Thanks,
Mohsen