VBA halts at first use of Worksheet object.

Question

I've written VBA to load data from a CSV file, copy it to a sheet, and then copy a portion of it to another sheet. It's used offsite by customers, but not commonly. One customer has reported a problem on two computers. This customer might be the only one
to have used the VBA since this bug developed. The workbook is copied to the installation directory by Inno Setup.
The problem is not consistently reproducible, except that once it appears it stays. It's resolved by making a new workbook with the same cell data and VBA. I haven't seen it manifest again after being resolved once.  The VBA encounters an error at the
first line where the information in the CSV and workbook actually matters. Unfortunately, I didn't make a note of the exact error at the last incident, but I think it was a null reference.
Without going into great detail, the logic triggering the error resembles this... (I would provide a minimal test case if I had a reproducible bug.)
Dim data As Worksheet ' CSV
Dim sheet As Worksheet ' XLSM
' halting here
data.Cells.Copy Destination:=sheet.Cells(1, 1)
This seems to be a problem with Excel's program state, somehow being written to and loaded from disk.
Is this familiar to anyone? Is there any likely cause I can investigate? I might not be able to use this information, as I'll be replacing the workbook in the installer.

Answer 1

It may be the size of the two sheets are the issue. I had something similar with sheets that were created as xls and used as xlsx, and vice-veras (I forget the exact details...)  Anyway, try limiting the copied cells:
data.Usedrange.Cells.Copy
Destination:=sheet.Cells(1,
1)