503 errors on some resources

In testing out web applications in Resin 3.0.18 some resources initially
throw a 503 error and then when we click on the link again the resource
is available. The error is reproducible and I was wondering if anyone
has had any run-ins with the same problem and had any solutions or work
arounds for it.

Configuration:
Apache-2.0.55
Resin 3.0.18 (with mod_caucho)
SunOS

Access Log
First attempt fails:
[09/Jun/2006:11:45:08 -0400] "POST /cba/home/index.do HTTP/1.1" 200 1137
[09/Jun/2006:11:45:08 -0400] "GET /help/RoboHelp_CSH.js HTTP/1.1" 304 -
[09/Jun/2006:11:45:08 -0400] "GET /cba/css/style.css HTTP/1.1" 503 323
<-----------
[09/Jun/2006:11:45:08 -0400] "GET /cba/images/z-dts-logo.gif HTTP/1.1"
304 -
[09/Jun/2006:11:45:08 -0400] "GET /cba/images/z-block02.gif HTTP/1.1"
304 -
[09/Jun/2006:11:45:08 -0400] "GET /cba/images/z-header.gif HTTP/1.1" 304
-
[09/Jun/2006:11:45:08 -0400] "GET /cba/images/z-nav_block-15.gif
HTTP/1.1" 304 -
[09/Jun/2006:11:45:08 -0400] "GET /cba/images/z-Untitled-2.gif HTTP/1.1"
304 -
[09/Jun/2006:11:45:08 -0400] "GET /cba/images/nav_block-750.gif
HTTP/1.1" 304 -
[09/Jun/2006:11:45:08 -0400] "GET /cba/images/toFunctions.gif HTTP/1.1"
304 -
[09/Jun/2006:11:45:08 -0400] "GET /cba/images/dtaFunctions.gif HTTP/1.1"
304 -
[09/Jun/2006:11:45:08 -0400] "GET /cba/images/pmoFunctions.gif HTTP/1.1"
304 -
Second attempt succeeds
[09/Jun/2006:11:45:24 -0400] "GET /cba/home/index.do HTTP/1.1" 200 1137
[09/Jun/2006:11:45:24 -0400] "GET /cba/css/style.css HTTP/1.1" 200 5352
<---------
...

I realize the first request starts with a  POST and the second request
starts with a GET but I know there are other resources that behave
similarly without that distinction, though I don't want to rule out any
potential reasons.

It doesn't always fail on CSS files either, it fails consistently and
repeatedly on a variety of resources.

Thanks for any help,
Kevin