SUMIF values in date range not working

Hi there, I've gotten this to work before but it's not now.

I'm trying to total the commissions for any sales made within a date range. For some reason, though I've entered the formula exactly how I believe it's worked before, isn't working. 

For example in the last sheet in the attached file, M7 is supposed to sum all amounts from Column D for any sales made between dates H7 and I7 ($500 total). Instead it's coming back with a totally wrong number, and I have no idea where it's pulling that total from. 

Please help.