Dynamic C 10.72 works with the 4000 and 5000 microprocessor.
The RCM3720 is a 3000 microprocessor, you will need to download the Dynamic C V9.62 from the link below: Once your on the page go to the section 'Development Software and Sample Code'
http://www.digi.com/support/productdetail?pid=5053&type=documentation