Recent revisions of the RCM4310 modules use a different serial flash, and it requires you to update your Dynamic C installation (so DC and RFU can use updated updated bootstrap code) and recompile your software to a new binary (so your program can access the serial flash).
Details here: http://knowledge.digi.com/articles/Knowledge_Base_Article/Serial-Flash-End-Of-Life-Patch-Support
The Dynamic C 10.72A installer includes that patch along with numerous bug fixes made since the release of 10.64. Digi has released Dynamic C on GitHub if you want to stay up to date with fixes as they're released.
https://github.com/digidotcom/DCRabbit_10