Calculate specific Date in powershell

Question

I'm a beginner in powershell

$test = ("=7*" + $newWorkSheet.Cells.Item($indexDate,9).Text + "+DATE(" + $newWorkSheet.Cells.Item($indexDate,8).Text + ";1;3)-WEEKDAY(DATE(" + $newWorkSheet.Cells.Item($indexDate,8).Text + ";1;3))-2")
$newWorkSheet.Cells.Item($indexDate,1) = $test

Result to an incomprehensive error : Exception de HRESULT : 0x800A03EC

this is what I want to put in my cell :

echo $test
=7*40+DATE(2014;1;3)-WEEKDAY(DATE(2014;1;3))-2

How can i resolve it ? Thx ! and sorry for my poor english :'(

Edit

I did :

$test = '=7*' + $newWorkSheet.Cells.Item($indexDate,9).Text + '+DATE(' + $newWorkSheet.Cells.Item($indexDate,8).Text + ';1;3)-WEEKDAY(DATE(' + $newWorkSheet.Cells.Item($indexDate,8).Text + ';1;3))-2'

if I echo $test I got what I want :

=7*40+DATE(2014;1;3)-WEEKDAY(DATE(2014;1;3))-2

but when i put $test into my cell like this :

$newWorkSheet.Cells.Item($indexDate,1) = $test

Result an error :

Exception de HRESULT : 0x800A03EC
Au caractère D:\Users\sadm\Documents\salesforce_1.ps1:839 : 1
+ $newWorkSheet.Cells.Item($indexDate,1) = $tmp1
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo          : OperationStopped: (:) [], COMException
+ FullyQualifiedErrorId : System.Runtime.InteropServices.COMException

Answer 1

I search to display a specific date with a number of week and a year.

Number of week and year are containing in cells of an excel.

$newWorkSheet.Cells.Item($indexDate,9) = $idsem ##Here is my number of week
$newWorkSheet.Cells.Item($indexDate,8) = $tempDate3.ToString("yyyy")
$test = "=" + "7*" + $newWorkSheet.Cells.Item($indexDate,9).Text + '+DATE(' + $newWorkSheet.Cells.Item($indexDate,8).Text + ';1;3)-JOURSEM(DATE(' + $newWorkSheet.Cells.Item($indexDate,8).Text + ';1;3))-2'
$newWorkSheet.Cells.Item($indexDate,1) = $test
$newWorkSheet.Cells.Item($indexDate,1).NumberFormat = "jj/mm/aaaa"
$global:indexDate++

When I launch the script with powershell 5.0 I had this error :

Exception de HRESULT : 0x800A03EC
Au caractère D:\Users\sadm\Documents\salesforce_1.ps1:831 : 1
+ $newWorkSheet.Cells.Item($indexDate,1) = $test
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo          : OperationStopped: (:) [], COMException
+ FullyQualifiedErrorId : System.Runtime.InteropServices.COMException

with 2.0 that works...