Run-time error '1004' with Range and copy

Hi,

Hopefully this is easy...

Running the following code I get a Run-time error '1004': Method 'Range' of Object '_worksheet' failed.

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The problem occurs at the highlighted code, however the first and last cells are referencing the correct cells in the ("Observation combinations") worksheet. The starting and ending cells are dynamically changed via a user input and therefore need to be calculated as shown; also the column is not fixed either.

Can you help?

Thanks,

Mbrolass.