Copy from a workbook to another workbook - vba

Question

I am having issues developing this code. I was able to develop the code to copy new data from my workbook to an existing path but am running into issues when trying to retrieve data from the existing path work book.
The concept is that there is a workbook in my system that will be collecting data. The data comes from different users that are working on project information. Once they have completed the project this new information along with existing information gets uploaded back to the workbook collecting that data. The work book collecting the data will always have a defined path. The workbooks that users are working off of will be in multiple places across the system.
The below macro keeps failing on the "Organizer.Sheets("Partnumber_Vendor_Database").Select". I am unsure why.
"Organizer" is the local database the user will use.
"Partnumber_Vendor_File" is the local database the information is stored.
If you can see that this code could be developed better please let me know! :)
Sub Find_Partnumber_Vendor_File()
' This sub is to open the partnumber_Vendor file to update the local database.
On Error Resume Next
Dim Organizer As Workbook
Set Organizer = Application.ActiveWorkbook
Dim Partnumber_Vendor_File As Workbook
Set Partnumber_Vendor_File = Workbooks.Open("S:\Supply Chain\PURCHASING\Forms and Templates\BOM Organizer\Partnumber_Vendor_File.xlsx")
If Err.Number = 1004 Then
MsgBox "Could not open. Check path in VBA"
Exit Sub
End If
If Partnumber_Vendor_File.ReadOnly Then
MsgBox "Sorry, partnumber to vendor database was already in use, try later"
Exit Sub
End If
On Error GoTo 0
Dim Data As Long
Data = ActiveSheet.Cells(Rows.count, 1).End(xlUp).Row
Range("A1:" & "D" & Data).Copy
Organizer.Sheets("Partnumber_Vendor_Database").Select
Range("A1:D1").Select
Selection.Insert Shift:=xlDown
Partnumber_Vendor_File.Close
End Sub

Answer 1

Althoug it is easy to use, avoid ActiveWorkbook, ActiveSheet and Sheets(<Title of the Sheet.).
The problem with the first two is that is hard to tell if the activeworkbook is actually the workbook you are looking for, specially when there are more than 1 workbook open. To workaround this, one solution is the use the Workbooks object to select the correct work book by its NAME (property CodeName). The Same for the Sheets, change the REAL NAMES of the Sheets so you can properlly call them.
The third is basically the same principle. In general, do not use titles of Sheets as references, use the REAL NAME of the object. Use the Property window in the VBA code to change that.
The error may come from 2 situations:
1 - Your selected workbook is not the actual workbook you want to work on.
2 - The Sheet "Partnumber_Vendor_Database" had its title changed or miswritten.
Hope it helps.