Screen Flashing When Solver is referred

[Satyadev]

We have Microsot Office Professional Plus 2007 installed.
I am working on a VB application which will opens a workbook and makes it
invisible. The file Test.xls doesn't have any macro or code except the
reference to SOLVER. When the code is executed it just flashes for a while
and then disappears.
When SOLVER is not reffered it is working perfectly and the excel sits in
the background as expected.
Please look at the following code snippet.

Dim exApp
Dim WK

set exApp= CreateObject("Excel.Application")
set WK=exApp.Workbooks.Open("C:\Test\Test.xls")
exApp.visible=false
exApp.DisplayAlerts=false

Please let us know what is causing for this flashing