I get this on my 877 evey now and again but just click retry or close SDM and re-connect and alls good - if the worst come to the worst reset the unit and re-config it using SDM but like myself you'll need to learn more on IOS as I think that the SDM although helpful in getting started is not a full config tool and may use defaults which are not suitable for your setup.
One last thing are you connecting by both the console and TCP/IP methods at the same time (this is where I noticed the prob mostly) e.g. console connection via serial and SDM connection via TCP/IP?
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...