Protecting certain cells using Vb.net

Hi!
I have an excel sheet and a windows form in visual studio 2013. The form allows users to enter data in excel sheet. It will be shared by multiple users. What I want to do is that certain cells in excel (eg: column B to G) should be locked but data entry in these cells should be allowed through the form. Once a user opens excel, they can edit other columns but not these columns. I locked the cells and protected the worksheet in excel. Then, in my vb code I added these:

Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
xlWorkBook = xlApp.Workbooks.Open("C:\Users\test.xlsx")
'xlApp.Visible = True
xlWorkSheet = xlWorkBook.Sheets("Sheet1")
xlWorkBook.Unprotect()

'entering data in excel

xlWorkBook.Save()
xlWorkBook.Protect()
End Sub
I get the error saying that 'the cells you are trying to enter data is protected.' something like this. What should I do? Please help!!

Originally Posted by Norie

Isn't it the worksheet you should be unprotecting rather than the workbook?

Yeah my bad. But I have changed it to xlWorksheet.Unprotect() and xlWorksheet.Protect(). Now it's allowing me to enter data but the problem is the protection is entirely removed. When i open excel the sheet is no longer protected. I want the sheet to be protected

My bad. I was saving before allowing to protect the file. Its done now!!
Thank you @Norie