here is some info:

Req:
POST http://............../proxyservlet/servlet/proxyservlet/BrowserService HTTP/1.1
Content-Type: x-application/hessian
Authorization: Basic ....................................................
User-Agent: Mozilla/4.0 (Windows XP 5.1) Java/1.6.0_05
Host: .................
Accept: text/html, image/gif, image/jpeg, ; q=.2, */; q=.2
Proxy-Connection: keep-alive
Transfer-Encoding: chunked

Res:
HTTP/1.0 501 Not Implemented
Server: squid/2.5.STABLE11
Mime-Version: 1.0
Date: Fri, 02 May 2008 08:49:43 GMT
Content-Type: text/html
Content-Length: 1131
Expires: Fri, 02 May 2008 08:49:43 GMT
X-Squid-Error: ERR_UNSUP_REQ 0
X-Cache: MISS from ..............
Proxy-Connection: close

So proxy reports that such a request is not supported. Because squid is "Squid is a fully-featured HTTP/1.0 proxy which is almost (but not quite - we're getting there!) HTTP/1.1 compliant." It might not support Transfer-Encoding: chunked introduced in HTTP/1.1.

Here is stack trace:

com.caucho.hessian.client.HessianConnectionException: 501: java.io.IOException: Server returned HTTP response code: 501 for URL: http://www2.edu.fi/proxyservlet/servlet/proxyservlet/BrowserService
at com.caucho.hessian.client.HessianProxy.invoke(HessianProxy.java:197)
at $Proxy0.getTreeOfPackages(Unknown Source)
at fi.nmi.neure.browser.BrowserDataController.getPackageFolderTree(BrowserDataController.java:67)
at fi.nmi.neure.browser.models.BrowserModel$2.construct(BrowserModel.java:172)
at javax.swing.swingutilities.SwingWorker$2.run(SwingWorker.java:109)
at java.lang.Thread.run(Unknown Source)
Caused by: java.io.IOException: Server returned HTTP response code: 501 for URL: http://www2.edu.fi/proxyservlet/servlet/proxyservlet/BrowserService
at sun.reflect.GeneratedConstructorAccessor13.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at sun.net.www.protocol.http.HttpURLConnection$6.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at sun.net.www.protocol.http.HttpURLConnection.getChainedException(Unknown Source)
at sun.net.www.protocol.http.HttpURLConnection.getInputStream(Unknown Source)
at com.caucho.hessian.client.HessianProxy.invoke(HessianProxy.java:179)
... 5 more
Caused by: java.io.IOException: Server returned HTTP response code: 501 for URL: http://www2.edu.fi/proxyservlet/servlet/proxyservlet/BrowserService
at sun.net.www.protocol.http.HttpURLConnection.getInputStream(Unknown Source)
at java.net.HttpURLConnection.getResponseCode(Unknown Source)
at com.caucho.hessian.client.HessianProxy.invoke(HessianProxy.java:168)
... 5 more