When getting a snapshot, w3wp process was stopped and snapshot could never be finished.
IIS monitors the health of the worker process for your application pool to ensure that it is responding to requests. When you press "Get Snapshot" button in dotMemory, profiler starts to collect application data and slows down your application on an appropriate amount of time, as a result, worker process doesn't respond in time and IIS terminates the process.
Please disable Worker Process Pinging for an Application Pool or change maximum response time. How to do it you can read in MSDN article: