Error 0x80300024: Installing Windows on SSD

I would like to install Windows 7 on an SSD for my MacbookPro (Mid-2012, still on Mountain Lion 😊). I want to continue using OSX most of the time and run Windows from time to time from the SSD.

I have a copy of the Windows 7 iso and drivers on a USB and am using Boot Camp, but every time I try to select the partition during the Windows installation I get an Error 0x80300024.

Is there a way to fix this error without having to erase the contents or repartition as free space my existing internal hard drive?

Thank you!