Your Computer is low on Memory. Program to close is vmware remote MKS

We are running ESXi 5.1. Users are connecting to VMs on ThinPCs, We have a handful of users reporting that they get the following error:

I have monitored the vm the user is connected to and they are not coming close to the memory limit. CPU usage is low. When the user click Close Program the error goes away, but tends to come back at random intervals. Other users in the same pool are working fine.

Any ideas?