Ora-12516

Which release of Windows are you running? 32-bit or 64-bit? How much RAM is installed? How much of that RAM is dedicated to your shared memory configuration for the database? Such errors are usually memory-related so it's likely that a memory handle has been lost or a semaphore can't be created to handle the work. TCP communication uses memory structures to hold the necessary connection information; you need to check your memory configuration for that server; it's likely that database services are consuming more resources than necessary which causes other memory to run short. This post doesn't address your problem directly but you might benefit from the script described in it:

https://dfitzjarrell.wordpress.com/2016/01/26/heap-of-trouble/

That script will show you where the shared memory is being used and how much of it is actually free, which can assist you in adjusting the memory settings for your database.

 

Your observations should include regular queries of V$MEMORY_TARGET_ADVICE as it will show you where you are (your current setting) as well as what changes to the current setting may give you in performance improvement. You need to read this post:

https://dfitzjarrell.wordpress.com/2015/03/30/sound-advice/

to understand how to use the advisors to your and your database's advantage.