I have various servers (dev, 2 x test, 2 x prod) running the same asp.net site.

The test and prod servers are in load-balanced pairs (prod1 with prod2, and test1 with test2).

The test server pair is exhibiting some kind of (super) slowdown or freezing during about one in ten page loads. Sometimes a line of text appears at the very top of the page which looks something like:

00 OK Date: Thu, 01 Apr 2010 01:50:09 GMT Server: Microsoft-IIS/6.0 X-Powered_By: ASP.NET X-AspNet-Version:2.0.50727 Cache-Control:private Content-Type:text/html; charset=ut

(the beginning and end are "cut off".)

Has anyone seen anything like this before? Any idea what it means or what's causing it?

Edit: I often see this too when clicking something - it comes up as red text on a yellow page:

XML Parsing Error: not well-formed
Location: http://203.111.46.211/3DSS/CompanyCompliance.aspx?cid=14
Line Number 1, Column 24:2mMTehON9OUNKySVaJ3ROpN" />
                         -----------------------^

If I go back and click again, it works (I see the page I clicked on, not the above error message).

Update:

...And, instead of the page loading, I sometimes just get a white screen with text like this in black (looks a lot like the above text):

HTTP/1.1 302 Found Date: Wed, 21 Apr 2010 04:53:39 GMT Server: Microsoft-IIS/6.0 X-Powered-By: ASP.NET X-AspNet-Version: 2.0.50727 Location: /3DSS/EditSections.aspx?id=3&siteId=56&sectionId=46 Set-Cookie: .3DSS=A6CAC223D0F2517D77C7C68EEF069ABA85E9392E93417FFA4209E2621B8DCE38174AD699C9F0221D30D49E108CAB8A828408CF214549A949501DAFAF59F080375A50162361E4AA94E08874BF0945B2EF; path=/; HttpOnly Cache-Control: private Content-Type: text/html; charset=utf-8 Content-Length: 184

object moved here

Where "here" is a link that points to a URL just like the one I'm requesting, except with an extra folder in it, meaning something like:
http://123.1.2.3/MySite//MySite/Page.aspx?option=1

instead of:
http://123.1.2.3/MySite/Page.aspx?option=1

Update:

A colleague of mine found some info saying it might be because the test servers are running iis in 64 bit (64bit win 2003) (prod servers are 32 bit win 2003).

So we tried telling IIS to use 32 bit:
**cscript %SYSTEMDRIVE%\inetpub\adminscripts\adsutil.vbs SET W3SVC/AppPools/Enable32bitAppOnWin64 1

%SYSTEMROOT%\Microsoft.NET\Framework\v2.0.50727\aspnet_regiis.exe -i **

(from this MS support page)

But iis stopped working altogether (got "server unavailable" on a white page instead of web sites).

Reversing the above (see the link) didn't work at first either. The ASP.NET tab disappeared from our IIS web site properties and we had to mess around for an hour uninstalling (aspnet_regiis.exe -u) and reinstalling 32 bit ASP.NET and adding Default.aspx manually back into default documents.

We'll probably try again in a few days, if anyone has anything to add in the meantime, please do.