Using a variable in a Formula: Quotes don't work

I have a dynamic range that I want to sum. I'm using lastRow to find the last row of data. The problem is that once I wrap the formula in quotes VBA does not recognize lastrow as a variable. I've tried all sorts of quote combinations - double quotes, triple quotes, apostrophes, etc. None seem to work. The code below does not work.

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It returns =SUM("A2:A" & lastrow) in cell G3.

Any help would be greatly appreciated.

You're missing the ampersand and quotation marks for the closing parenthesis and another one quotation mark just after A""

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Thank you. I added these; lastRow is now recognized (it changes to an uppercase 'R' as in the Dim), but I'm still getting a runtime error 1004 on that line. Could it have something to do with the version of Excel that I'm using right now (Excel 2007)? Is there a way around this?

Thank you. That works. And thank you for the advice about using Long.