@bawh03 welcome to the KNIME forum. Could you give us more details about what you are doing and when this problem might occur. If possible you might create a Logfile in DEBUG mode to give us more insight.
What kind of data operations are you doing, how large is the data compared to your 20GB of RAM - how much is your overall RAM and are there other processes running?
Also concerning performance you might want to read this article: