I must admit that we never saw this type of error in this context. We've been testing a lot of hosting services lately, and are confident that MonoX is neither leaking memory nor consuming huge amounts of memory. I would say that system resources are spread too thin for all the sites on the machine you are using.
You may consider using another hosting provider. Please visit our blog for a series of reviews of hosting services we recommend. For a shared hosting scenario I would recommend
Arvixe, as it comes with MonoX preinstalled for only $5 per month (unlimited storage and databases).