Help on Monthly Summary (File attached)

Good morning everyone. I am trying to create a monthly summary from multiple worksheets. There are 2 macros here one to generate a new daily rental sheet this works flawlessly, the second one that generates the monthly summary isn't auto summing correctly. The formula in there is =SUM(first:last!C7), I found the formula that works it is ='07-June-2013'!C7+'10-Jun-2013'!C7. I do not know how to program the macro to use this autosum when the Monthly Summary button is hit. This needs to autosum for each sheet created.

Thanks in Advance.