Solution is written in your post.
To resolve this, either reduce the load on the machine or adjust the
value of minFreeMemoryPercentageToActivateService on the
serviceHostingEnvironment config element.
The easiest way just add this into your web.config
<system.serviceModel>
<serviceHostingEnvironment minFreeMemoryPercentageToActivateService="0" />
</system.serviceModel>
Read more about serviceHostingEnvironment
here.
Anyway how @Mr Grok correctly pointed it is an indication that your machine doesn’t have enough physical memory and you should figure out why is this happening. It can be a serious problem.