some strange and blocking problems with varnish

[Daniel]

Hi,

first i want to say that varnish is a great program. But i have to say that we 
have some problems so we have to switch back to squid temporary.

We use varnish 1.1 in front of pound (loadbalancer) and behind this the real 
webservers (apache 2.2 with mod_rewrite, php, ...)

First Problem that appeared:
We host a vbulletin forum and with switching to varnish the login didn't work 
correctly anymore. You could login and you were listed as logged in, but the 
page looks like you're logged out. If you activated the "Remember Me?" 
checkbox, it worked. 
We have tested several configurations:
- pass/pipe everything of this domain
- added the server directly as backend
- played with caching or not caching cookie sites

Now we set the domain directly to the backend webserver. We haven't found a 
solution yet.

Second problem:
varnish produces Internal Server errors though the requested site is 
available, if i go through pound->backend webserver or directly to the 
backend servers. One url was unavailable for several hours. One of 100 wget 
requests ended with a success, but before and after this one only errors. Now 
this one works again, but we get still nearly randomly internal server 
errors. No matter how many request have to be handled by varnish.

Here my configurations, perhaps there's a fault:
vcl: http://pastebin.com/f4aa96552
daemon opts: http://pastebin.com/f5055076c

I hope you can help me to solve these things. Atm it's not possible to enable 
vcl_trace since there are around 200 req/s. I think we'll switch back to 
squid tomorrow, so i'll be able to trace the problem better.

Kind Regards,
Daniel