You should include error handling in all your VB or VBA code. Here's a simple but effective way to do so. I am relatively new to VBA (Java/Python are more my thing, along with Haskell). One thing that has shocked and surprised me about VBA is the lack of any "obvious" way to do proper structured error handling.
Private Sub CommandButton_Click()
On Error GoTo err_handler
Problem: The code appears to cause Excel to sometimes crash. Not all the time.
In Excel 97, this doesn't happen at all.
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