SUM Formula Erring

In the following routine I keep getting an Application or Object Defined Error when it reaches the code highlighted in red below. My string variables are returning the correct cell addresses. I know this because I replaced the "Formula" line with the following line and it returns what I need.

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I just can't seem to get this into the "=SUM()" Formula. Any help would be appreciated.

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Try this

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You need to get the speech marks in the correct place. If you are using variables as in your example then the variables do not need the speech marks.