fix: Improve Excel file conversion with SaveAs2 and robust path handling

SharePointFunctions.ps1

@@ -484,17 +484,40 @@ function Convert-Files {
                 $excel.DisplayAlerts = $false  # Suppress Excel alerts
                 
                 try {
-                    $workbook = $excel.Workbooks.Open($downloadPath)
+                    # Convert paths to proper format for Excel
+                    $excelDownloadPath = $downloadPath -replace "\\", "\\"
+                    $excelXlsxPath = $xlsxPath -replace "\\", "\\"
+                    
+                    $workbook = $excel.Workbooks.Open($excelDownloadPath)
+                    
+                    # Save as XLSX using Excel constants
+                    $xlOpenXMLWorkbook = 51  # Excel constant for XLSX format
+                    $xlNormal = 1  # Excel constant for normal save
+                    
+                    # Use the Excel Application SaveAs2 method
+                    $workbook.SaveAs2(
+                        $excelXlsxPath,
+                        $xlOpenXMLWorkbook,  # FileFormat = xlsx
+                        $null,              # Password
+                        $null,              # WriteResPassword
+                        $false,             # ReadOnlyRecommended
+                        $null,              # CreateBackup
+                        $xlNormal,          # AccessMode
+                        $null,              # ConflictResolution
+                        $true,              # AddToMru
+                        $null,              # TextCodepage
+                        $null,              # TextVisualLayout
+                        $false              # Local
+                    )
                     
-                    # Save as XLSX using the full path
-                    $workbook.SaveAs([string]$xlsxPath, 51)  # 51 = xlOpenXMLWorkbook (*.xlsx)
                     $workbook.Close($true)  # True to save changes
                     
-                    Start-Sleep -Seconds 1  # Give Excel time to finish saving
+                    Start-Sleep -Seconds 2  # Give Excel more time to finish saving
                     
-                    # Verify the file was created
-                    if (-not (Test-Path -LiteralPath $xlsxPath)) {
-                        throw "Excel SaveAs succeeded but file not found at: $xlsxPath"
+                    # Verify the file was created using robust path checking
+                    $verifyPath = [System.IO.Path]::GetFullPath($xlsxPath)
+                    if (-not (Test-Path -LiteralPath $verifyPath)) {
+                        throw "Excel SaveAs succeeded but file not found at: $verifyPath"
                     }
                 }
                 finally {
@@ -506,6 +529,9 @@ function Convert-Files {
                     [System.Runtime.Interopservices.Marshal]::ReleaseComObject($excel) | Out-Null
                     [System.GC]::Collect()
                     [System.GC]::WaitForPendingFinalizers()
+                    
+                    # Force Excel process cleanup
+                    Get-Process -Name "EXCEL" -ErrorAction SilentlyContinue | Where-Object { $_.SI -eq [System.Security.Principal.WindowsIdentity]::GetCurrent().SessionId } | Stop-Process -Force
                 }
                 
                 $script:txtStatus.Text += "Successfully converted to: $xlsxFileName`n"