VBA Code Works Great Until Number Of Rows Changed

I wrote the following basic code earlier (which will end up being part of a larger code)

Code:
Dim DateInput As String
Dim LastCell As String

Sub LastRowInputBox()

LastCell = InputBox("What is the last row number in the range?", "Last Row Input")

[Code] ......

As you can see, all the ColumnCopyInsert Subroutine does is copy select/copy four columns (E:H), inserts the copied selection immediately to the right, inserts formulas and autofills down to the last row required. I added the LastRowInputBox routine as the range of rows varies from week to week (inserting new rows, deleting others).

The code works great...up to a point unfortunately. If ran as it is, everything that should be copied/pasted will be and cells autofilled to the row specified via the InputBox. Here comes the problem, if any rows are either inserted or deleted then the code throws out "The object invoked has disconnected from its clients" when it reaches the first instance of the following line:

Code:
Selection.Insert Shift:=xlToRight

At which point, Excel hangs (or maybe in some sort of loop) and I have to open Device Manager and close the Excel exe process.