503 errors

[Mark E]

Hi,

Anyone know why Varnish would throw a "503 Guru Mediation" error when 
landing on site that uses cookies? For example, we have a WordPress site 
that of course requires login to reach the admin interface. Every so 
often anyone who has ever logged in sees the 503 error. The only way 
around it that I know of so far is to clear the cookie by either 
deleting it or going to the WordPress login screen which runs a bit of 
code to clear the cookie. Or at least that's what I think is happening.

The VCL isn't caching pages with cookies.

How do I remedy this issue?

Mark