Hi there ... new to this world and just spent some time leaning a lesson..
I have a just built a Adafruit DS1307 RTC ... tested it on Sparkfun Red Board -- Arduino Uno equivalent -- all worked fine.
So I moved to a Netduino Plus .. no luck as I believe it is a problem with the upgrade to NetMF 4.2 So I move to my new NetDunio Plus 2. (NP2) Still no luck. ugh!
After several false starts and several different code samples, I finally check the forum and discovered the above posts. Based on this I got it to work.
The issue is using the analog A4/A5 vs SDA/SCL pins. On the Sparkfun Red board, you can use either the A4/A5 or SDA/SCL pin and either set works. On the Netduino Plus you must use A4/A5 as no explicit SDA/SCL exist.
On the NP2, it appears you must use the SDA/SCL pins. I had moved from the Red board, to the Netduino Plus and move the pins to the same pins as I had used on the Red Board, then discovered issue related to 4.2 update, so moved to NP2 using the same pins as before - A4/A5/Gnd/V5 - with no luck.
Bottom line - all is working using SDA/SCL/Gnd/V5 on the NP2.
Hope this helps others who are just starting out .. Any comments or insights would be appreciated.
Paul.